diff --git a/explorer/file_test.cpp b/explorer/file_test.cpp
index 9107de492748..10f2c696c2cf 100644
--- a/explorer/file_test.cpp
+++ b/explorer/file_test.cpp
@@ -75,15 +75,12 @@ class ExplorerFileTest : public FileTestBase {
     return args;
   }
 
-  auto GetLineNumberReplacement(llvm::ArrayRef<llvm::StringRef> filenames)
-      -> LineNumberReplacement override {
+  auto GetLineNumberReplacements(llvm::ArrayRef<llvm::StringRef> filenames)
+      -> llvm::SmallVector<LineNumberReplacement> override {
     if (check_trace_output()) {
-      return {.has_file = false,
-              .pattern = R"((DO NOT MATCH))",
-              // The `{{{{` becomes `{{`.
-              .line_formatv = "{{{{ *}}{0}"};
+      return {};
     }
-    return FileTestBase::GetLineNumberReplacement(filenames);
+    return FileTestBase::GetLineNumberReplacements(filenames);
   }
 
   auto DoExtraCheckReplacements(std::string& check_line) -> void override {
diff --git a/testing/file_test/autoupdate.cpp b/testing/file_test/autoupdate.cpp
index b945e42feea6..b7a87f369c8d 100644
--- a/testing/file_test/autoupdate.cpp
+++ b/testing/file_test/autoupdate.cpp
@@ -13,7 +13,6 @@
 #include "llvm/ADT/STLFunctionalExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/FormatVariadic.h"
-#include "re2/re2.h"
 
 namespace Carbon::Testing {
 
@@ -26,20 +25,34 @@ static auto ParseLineNumber(absl::string_view matched_line_number) -> int {
   trimmed = trimmed.trim();
   // NOLINTNEXTLINE(google-runtime-int): API requirement.
   long long val;
-  CARBON_CHECK(!llvm::getAsSignedInteger(trimmed, 10, val));
+  CARBON_CHECK(!llvm::getAsSignedInteger(trimmed, 10, val))
+      << matched_line_number;
   return val;
 }
 
+// The file and line number that a CHECK line refers to, and the
+// replacement from which they were determined, if any.
+struct FileAndLineNumber {
+  explicit FileAndLineNumber(int file_number) : file_number(file_number) {}
+
+  explicit FileAndLineNumber(const FileTestLineNumberReplacement* replacement,
+                             int file_number, absl::string_view line_number)
+      : replacement(replacement),
+        file_number(file_number),
+        line_number(ParseLineNumber(line_number)) {}
+
+  const FileTestLineNumberReplacement* replacement = nullptr;
+  int file_number;
+  int line_number = -1;
+};
+
 class CheckLine : public FileTestLineBase {
  public:
   // RE2 is passed by a pointer because it doesn't support std::optional.
-  explicit CheckLine(int file_number, int line_number,
-                     bool line_number_re_has_file, const RE2* line_number_re,
-                     std::string line)
-      : FileTestLineBase(line_number),
-        file_number_(file_number),
-        line_number_re_has_file_(line_number_re_has_file),
-        line_number_re_(line_number_re),
+  explicit CheckLine(FileAndLineNumber file_and_line_number, std::string line)
+      : FileTestLineBase(file_and_line_number.line_number),
+        file_number_(file_and_line_number.file_number),
+        replacement_(file_and_line_number.replacement),
         line_(std::move(line)) {}
 
   auto Print(llvm::raw_ostream& out) const -> void override {
@@ -57,32 +70,31 @@ class CheckLine : public FileTestLineBase {
 
   // When the location of all lines in a file are known, we can set the line
   // offset based on the target line.
-  auto RemapLineNumbers(const std::string& line_formatv,
-                        llvm::function_ref<int(int)> line_remap) -> void {
-    // Only need to do remappings when there's a regex.
-    if (!line_number_re_) {
-      return;
-    }
-
-    // If the CHECK was written to a different file from the file that it refers
-    // to, leave behind an absolute line reference rather than a cross-file
-    // offset.
-    // TODO: We should also remap cross-file line references so that we don't
-    // need multiple runs of autoupdate for the output to stabilize.
-    if (output_file_number_ != file_number_) {
+  auto RemapLineNumbers(
+      const llvm::DenseMap<std::pair<int, int>, int>& output_line_remap,
+      const llvm::SmallVector<int>& new_last_line_numbers) -> void {
+    // Only need to do remappings when there's a line number replacement.
+    if (!replacement_) {
       return;
     }
 
     bool found_one = false;
+    // Use a cursor for the line so that we can't keep matching the same
+    // content, which may occur when we keep a literal line number.
+    int line_offset = 0;
     while (true) {
+      // Rebuild the cursor each time because we're editing the line, which
+      // could cause a reallocation.
+      absl::string_view line_cursor = line_;
+      line_cursor.remove_prefix(line_offset);
       // Look for a line number to replace. There may be multiple, so we
       // repeatedly check.
       absl::string_view matched_line_number;
-      if (line_number_re_has_file_) {
-        RE2::PartialMatch(line_, *line_number_re_, nullptr,
+      if (replacement_->has_file) {
+        RE2::PartialMatch(line_cursor, *replacement_->re, nullptr,
                           &matched_line_number);
       } else {
-        RE2::PartialMatch(line_, *line_number_re_, &matched_line_number);
+        RE2::PartialMatch(line_cursor, *replacement_->re, &matched_line_number);
       }
       if (matched_line_number.empty()) {
         CARBON_CHECK(found_one) << line_;
@@ -90,29 +102,50 @@ class CheckLine : public FileTestLineBase {
       }
       found_one = true;
 
-      // Calculate the offset from the CHECK line to the new line number
-      // (possibly with new CHECK lines added, or some removed).
-      int new_line_number = line_remap(ParseLineNumber(matched_line_number));
-      int offset = new_line_number - output_line_number_;
+      // Update the cursor offset from the match.
+      line_offset = matched_line_number.begin() - line_.c_str();
 
-      // Update the line offset in the CHECK line.
-      const char* offset_prefix = offset < 0 ? "" : "+";
-      std::string replacement = llvm::formatv(
-          line_formatv.c_str(),
-          llvm::formatv("[[@LINE{0}{1}]]", offset_prefix, offset));
+      // Calculate the new line number (possibly with new CHECK lines added, or
+      // some removed).
+      int old_line_number = ParseLineNumber(matched_line_number);
+      int new_line_number = -1;
+      if (auto remapped =
+              output_line_remap.find({file_number_, old_line_number});
+          remapped != output_line_remap.end()) {
+        // Map old non-check lines to their new line numbers.
+        new_line_number = remapped->second;
+      } else {
+        // We assume unmapped references point to the end-of-file.
+        new_line_number = new_last_line_numbers[file_number_];
+      }
+
+      std::string replacement;
+      if (output_file_number_ == file_number_) {
+        int offset = new_line_number - output_line_number_;
+        // Update the line offset in the CHECK line.
+        const char* offset_prefix = offset < 0 ? "" : "+";
+        replacement = llvm::formatv(
+            replacement_->line_formatv.c_str(),
+            llvm::formatv("[[@LINE{0}{1}]]", offset_prefix, offset));
+      } else {
+        // If the CHECK was written to a different file from the file that it
+        // refers to, leave behind an absolute line reference rather than a
+        // cross-file offset.
+        replacement =
+            llvm::formatv(replacement_->line_formatv.c_str(), new_line_number);
+      }
       line_.replace(matched_line_number.data() - line_.data(),
                     matched_line_number.size(), replacement);
     }
   }
 
-  int file_number() const { return file_number_; }
+  auto file_number() const -> int { return file_number_; }
 
   auto is_blank() const -> bool override { return false; }
 
  private:
   int file_number_;
-  bool line_number_re_has_file_;
-  const RE2* line_number_re_;
+  const FileTestLineNumberReplacement* replacement_;
   std::string line_;
   llvm::StringRef indent_;
   int output_file_number_ = -1;
@@ -121,11 +154,45 @@ class CheckLine : public FileTestLineBase {
 
 }  // namespace
 
+// Looks for the patterns in the line. Returns the first match, or defaulted
+// information if not found.
+static auto GetFileAndLineNumber(
+    const llvm::SmallVector<FileTestLineNumberReplacement>& replacements,
+    llvm::DenseMap<llvm::StringRef, int> file_to_number_map,
+    int default_file_number, const std::string& check_line)
+    -> FileAndLineNumber {
+  for (const auto& replacement : replacements) {
+    if (replacement.has_file) {
+      absl::string_view filename;
+      absl::string_view line_number;
+      if (RE2::PartialMatch(check_line, *replacement.re, &filename,
+                            &line_number)) {
+        if (auto it = file_to_number_map.find(filename);
+            it != file_to_number_map.end()) {
+          return FileAndLineNumber(&replacement, it->second, line_number);
+        } else {
+          return FileAndLineNumber(default_file_number);
+        }
+      }
+    } else {
+      // There's no file association, so we only look at the line, and assume
+      // it refers to the default file.
+      absl::string_view line_number;
+      if (RE2::PartialMatch(check_line, *replacement.re, &line_number)) {
+        return FileAndLineNumber(&replacement, default_file_number,
+                                 line_number);
+      }
+    }
+  }
+  return FileAndLineNumber(default_file_number);
+}
+
 // Builds CheckLine lists for autoupdate.
 static auto BuildCheckLines(
     llvm::StringRef output, const char* label,
     const llvm::SmallVector<llvm::StringRef>& filenames,
-    bool line_number_re_has_file, const RE2& line_number_re,
+    const std::optional<RE2>& default_file_re,
+    const llvm::SmallVector<FileTestLineNumberReplacement>& replacements,
     std::function<void(std::string&)> do_extra_check_replacements)
     -> llvm::SmallVector<CheckLine> {
   llvm::SmallVector<CheckLine> check_lines;
@@ -157,6 +224,9 @@ static auto BuildCheckLines(
   // End-of-line whitespace is replaced with a regex matcher to make it visible.
   RE2 end_of_line_whitespace_re(R"((\s+)$)");
 
+  // The default file number for when no specific file is found.
+  int default_file_number = 0;
+
   for (const auto& line : lines) {
     std::string check_line = llvm::formatv("// CHECK:{0}:{1}{2}", label,
                                            line.empty() ? "" : " ", line);
@@ -171,32 +241,19 @@ static auto BuildCheckLines(
 
     do_extra_check_replacements(check_line);
 
-    // Look for line information in the output. use_line_number is only set if
-    // the match is correct.
-    std::optional<llvm::StringRef> use_line_number;
-    absl::string_view match_line_number;
-    int file_number = 0;
-    if (line_number_re_has_file) {
-      absl::string_view match_filename;
-      if (RE2::PartialMatch(check_line, line_number_re, &match_filename,
-                            &match_line_number)) {
-        if (auto it = file_to_number_map.find(match_filename);
-            it != file_to_number_map.end()) {
-          file_number = it->second;
-          use_line_number = match_line_number;
-        }
-      }
-    } else {
-      // There's no file association, so we only look at the line, and assume it
-      // refers to the main file.
-      if (RE2::PartialMatch(check_line, line_number_re, &match_line_number)) {
-        use_line_number = match_line_number;
+    if (default_file_re) {
+      absl::string_view filename;
+      if (RE2::PartialMatch(line, *default_file_re, &filename)) {
+        auto it = file_to_number_map.find(filename);
+        CARBON_CHECK(it != file_to_number_map.end())
+            << "default_file_re had unexpected match in '" << line << "' (`"
+            << default_file_re->pattern() << "`)";
+        default_file_number = it->second;
       }
     }
-    int line_number = use_line_number ? ParseLineNumber(*use_line_number) : -1;
-    check_lines.push_back(
-        CheckLine(file_number, line_number, line_number_re_has_file,
-                  use_line_number ? &line_number_re : nullptr, check_line));
+    auto file_and_line = GetFileAndLineNumber(replacements, file_to_number_map,
+                                              default_file_number, check_line);
+    check_lines.push_back(CheckLine(file_and_line, check_line));
   }
 
   return check_lines;
@@ -206,21 +263,27 @@ auto AutoupdateFileTest(
     const std::filesystem::path& file_test_path, llvm::StringRef input_content,
     const llvm::SmallVector<llvm::StringRef>& filenames,
     int autoupdate_line_number,
-    llvm::SmallVector<llvm::SmallVector<FileTestLine>>& non_check_lines,
+    const llvm::SmallVector<llvm::SmallVector<FileTestLine>>& non_check_lines,
     llvm::StringRef stdout, llvm::StringRef stderr,
-    FileTestLineNumberReplacement line_number_replacement,
+    const std::optional<RE2>& default_file_re,
+    const llvm::SmallVector<FileTestLineNumberReplacement>&
+        line_number_replacements,
     std::function<void(std::string&)> do_extra_check_replacements) -> bool {
-  RE2 line_number_re(line_number_replacement.pattern);
-  CARBON_CHECK(line_number_re.ok()) << "Invalid line replacement RE2: `"
-                                    << line_number_replacement.pattern << "`";
+  for (const auto& replacement : line_number_replacements) {
+    CARBON_CHECK(replacement.has_file || default_file_re)
+        << "For replacement with pattern `" << replacement.re->pattern()
+        << "` to have has_file=false, override GetDefaultFileRE.";
+    CARBON_CHECK(replacement.re->ok())
+        << "Invalid line replacement RE2: " << replacement.re->error();
+  }
 
   // Prepare CHECK lines.
-  llvm::SmallVector<CheckLine> stdout_check_lines = BuildCheckLines(
-      stdout, "STDOUT", filenames, line_number_replacement.has_file,
-      line_number_re, do_extra_check_replacements);
-  llvm::SmallVector<CheckLine> stderr_check_lines = BuildCheckLines(
-      stderr, "STDERR", filenames, line_number_replacement.has_file,
-      line_number_re, do_extra_check_replacements);
+  llvm::SmallVector<CheckLine> stdout_check_lines =
+      BuildCheckLines(stdout, "STDOUT", filenames, default_file_re,
+                      line_number_replacements, do_extra_check_replacements);
+  llvm::SmallVector<CheckLine> stderr_check_lines =
+      BuildCheckLines(stderr, "STDERR", filenames, default_file_re,
+                      line_number_replacements, do_extra_check_replacements);
   auto* stdout_check_line = stdout_check_lines.begin();
   auto* stderr_check_line = stderr_check_lines.begin();
 
@@ -233,15 +296,23 @@ auto AutoupdateFileTest(
 
   const FileTestLine blank_line(-1, "");
 
+  // Maps {file_number, original line number} to a new line number.
+  llvm::DenseMap<std::pair<int, int>, int> output_line_remap;
+
+  // Tracks the new last line numbers for each file.
+  llvm::SmallVector<int> new_last_line_numbers;
+  new_last_line_numbers.reserve(filenames.size());
+
   // Stitch together content.
   llvm::SmallVector<const FileTestLineBase*> new_lines;
   for (auto [file_number_as_size_t, filename, non_check_file] :
        llvm::enumerate(filenames, non_check_lines)) {
     auto file_number = static_cast<int>(file_number_as_size_t);
-    llvm::DenseMap<int, int> output_line_remap;
-    llvm::SmallVector<CheckLine*> check_lines_this_file;
     int output_line_number = 0;
 
+    // Track the offset in new_lines to later determine the line count.
+    int file_offset_in_new_lines = new_lines.size();
+
     // Add all check lines from the given vector until we reach a check line
     // attached to a line later than `to_line_number`.
     auto add_check_lines = [&](const llvm::SmallVector<CheckLine>& lines,
@@ -253,7 +324,6 @@ auto AutoupdateFileTest(
            ++line) {
         new_lines.push_back(line);
         line->SetOutputLine(indent, file_number, ++output_line_number);
-        check_lines_this_file.push_back(line);
       }
     };
 
@@ -264,6 +334,10 @@ auto AutoupdateFileTest(
       // something like a split directive which shouldn't increment
       // output_line_number.
       if (non_check_line.line_number() < 1) {
+        // These are ignored when calculating line counts.
+        CARBON_CHECK(file_offset_in_new_lines ==
+                     static_cast<int>(new_lines.size()));
+        ++file_offset_in_new_lines;
         new_lines.push_back(&non_check_line);
         continue;
       }
@@ -281,10 +355,10 @@ auto AutoupdateFileTest(
       }
 
       new_lines.push_back(&non_check_line);
-      CARBON_CHECK(
-          output_line_remap
-              .insert({non_check_line.line_number(), ++output_line_number})
-              .second);
+      CARBON_CHECK(output_line_remap
+                       .insert({{file_number, non_check_line.line_number()},
+                                ++output_line_number})
+                       .second);
 
       // If we just added the AUTOUPDATE line, include any early STDERR lines
       // now, so that the initial batch of CHECK lines have STDERR before
@@ -306,11 +380,12 @@ auto AutoupdateFileTest(
     // This should always be true after the first file is processed.
     CARBON_CHECK(reached_autoupdate);
 
-    // At the end of the last file, print remaining check lines which -- for
-    // whatever reason -- come after all original lines.
-    if (file_number == static_cast<int>(filenames.size()) - 1 &&
-        (stderr_check_line != stderr_check_lines.end() ||
-         stdout_check_line != stdout_check_lines.end())) {
+    // At the end of each file, print any remaining lines which are associated
+    // with the file.
+    if ((stderr_check_line != stderr_check_lines.end() &&
+         stderr_check_line->file_number() == file_number) ||
+        (stdout_check_line != stdout_check_lines.end() &&
+         stdout_check_line->file_number() == file_number)) {
       // Ensure there's a blank line before any trailing CHECKs.
       if (!new_lines.empty() && !new_lines.back()->is_blank()) {
         new_lines.push_back(&blank_line);
@@ -321,30 +396,15 @@ auto AutoupdateFileTest(
       add_check_lines(stdout_check_lines, stdout_check_line, INT_MAX, "");
     }
 
-    // Update all remapped lines in CHECK output.
-    for (auto* offset_check_line : check_lines_this_file) {
-      int last_non_check_line = non_check_file.back().line_number();
-      offset_check_line->RemapLineNumbers(
-          line_number_replacement.line_formatv, [&](int old_line_number) {
-            // Map old non-check lines to their new line numbers.
-            auto remapped = output_line_remap.find(old_line_number);
-            if (remapped != output_line_remap.end()) {
-              return remapped->second;
-            }
+    new_last_line_numbers.push_back(new_lines.size() -
+                                    file_offset_in_new_lines);
+  }
 
-            // Map any reference to a line past the final non-check line to
-            // the new end-of-file. We assume that any such reference is
-            // referring to the end of file, not to some specific CHECK
-            // comment.
-            if (old_line_number > last_non_check_line) {
-              return output_line_number;
-            }
-
-            // Line didn't get remapped; maybe it refers to a CHECK line.
-            // We can't express that as an offset, just leave it as-is.
-            return old_line_number;
-          });
-    }
+  for (auto& check_line : stdout_check_lines) {
+    check_line.RemapLineNumbers(output_line_remap, new_last_line_numbers);
+  }
+  for (auto& check_line : stderr_check_lines) {
+    check_line.RemapLineNumbers(output_line_remap, new_last_line_numbers);
   }
 
   // Generate the autoupdated file.
diff --git a/testing/file_test/autoupdate.h b/testing/file_test/autoupdate.h
index c0c81165795a..cdc4956cfc6d 100644
--- a/testing/file_test/autoupdate.h
+++ b/testing/file_test/autoupdate.h
@@ -9,6 +9,7 @@
 
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "re2/re2.h"
 #include "testing/file_test/line.h"
 
 namespace Carbon::Testing {
@@ -17,8 +18,11 @@ struct FileTestLineNumberReplacement {
   bool has_file;
 
   // The line replacement. The pattern should match lines. If has_file, pattern
-  // should have a file and line group; otherwise, only a line group.
-  std::string pattern;
+  // should have a file and line group; otherwise, only a line group, but
+  // default_file_re should be provided.
+  //
+  // Uses shared_ptr for storage in SmallVector.
+  std::shared_ptr<RE2> re;
 
   // line_formatv should provide {0} to substitute with [[@LINE...]] deltas.
   std::string line_formatv;
@@ -29,9 +33,11 @@ auto AutoupdateFileTest(
     const std::filesystem::path& file_test_path, llvm::StringRef input_content,
     const llvm::SmallVector<llvm::StringRef>& filenames,
     int autoupdate_line_number,
-    llvm::SmallVector<llvm::SmallVector<FileTestLine>>& non_check_lines,
+    const llvm::SmallVector<llvm::SmallVector<FileTestLine>>& non_check_lines,
     llvm::StringRef stdout, llvm::StringRef stderr,
-    FileTestLineNumberReplacement line_number_replacement,
+    const std::optional<RE2>& default_file_re,
+    const llvm::SmallVector<FileTestLineNumberReplacement>&
+        line_number_replacements,
     std::function<void(std::string&)> do_extra_check_replacements) -> bool;
 
 }  // namespace Carbon::Testing
diff --git a/testing/file_test/autoupdate_testdata.sh b/testing/file_test/autoupdate_testdata.sh
new file mode 100755
index 000000000000..cbf3312de1ff
--- /dev/null
+++ b/testing/file_test/autoupdate_testdata.sh
@@ -0,0 +1,7 @@
+#!/usr/bin/env bash
+
+# Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+# Exceptions. See /LICENSE for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+bazel run -c opt //testing/file_test:file_test_base_test -- --autoupdate "$@"
diff --git a/testing/file_test/file_test_base.cpp b/testing/file_test/file_test_base.cpp
index 087042864f9e..c7ca372771fd 100644
--- a/testing/file_test/file_test_base.cpp
+++ b/testing/file_test/file_test_base.cpp
@@ -6,6 +6,7 @@
 
 #include <filesystem>
 #include <fstream>
+#include <optional>
 #include <string>
 #include <utility>
 
@@ -109,25 +110,26 @@ auto FileTestBase::Autoupdate() -> ErrorOr<bool> {
     filenames.push_back(file.filename);
   }
 
-  llvm::ArrayRef filenames_for_line_number = filenames;
+  llvm::ArrayRef expected_filenames = filenames;
   if (filenames.size() > 1) {
-    filenames_for_line_number = filenames_for_line_number.drop_front();
+    expected_filenames = expected_filenames.drop_front();
   }
 
   return AutoupdateFileTest(
       std::filesystem::absolute(test_name_.str()), context.input_content,
       filenames, *context.autoupdate_line_number, context.non_check_lines,
-      context.stdout, context.stderr,
-      GetLineNumberReplacement(filenames_for_line_number),
+      context.stdout, context.stderr, GetDefaultFileRE(expected_filenames),
+      GetLineNumberReplacements(expected_filenames),
       [&](std::string& line) { DoExtraCheckReplacements(line); });
 }
 
-auto FileTestBase::GetLineNumberReplacement(
-    llvm::ArrayRef<llvm::StringRef> filenames) -> LineNumberReplacement {
-  return {
-      .has_file = true,
-      .pattern = llvm::formatv(R"(({0}):(\d+))", llvm::join(filenames, "|")),
-      .line_formatv = R"({0})"};
+auto FileTestBase::GetLineNumberReplacements(
+    llvm::ArrayRef<llvm::StringRef> filenames)
+    -> llvm::SmallVector<LineNumberReplacement> {
+  return {{.has_file = true,
+           .re = std::make_shared<RE2>(
+               llvm::formatv(R"(({0}):(\d+))", llvm::join(filenames, "|"))),
+           .line_formatv = R"({0})"}};
 }
 
 auto FileTestBase::ProcessTestFileAndRun(TestContext& context)
@@ -501,4 +503,6 @@ static auto Main(int argc, char** argv) -> int {
 
 }  // namespace Carbon::Testing
 
-auto main(int argc, char** argv) -> int { Carbon::Testing::Main(argc, argv); }
+auto main(int argc, char** argv) -> int {
+  return Carbon::Testing::Main(argc, argv);
+}
diff --git a/testing/file_test/file_test_base.h b/testing/file_test/file_test_base.h
index a4c3f39d4381..9d008dfc7b34 100644
--- a/testing/file_test/file_test_base.h
+++ b/testing/file_test/file_test_base.h
@@ -66,10 +66,19 @@ class FileTestBase : public testing::Test {
   // Returns default arguments. Only called when a file doesn't set ARGS.
   virtual auto GetDefaultArgs() -> llvm::SmallVector<std::string> = 0;
 
+  // Returns a regex to match the default file when a line may not be present.
+  // May return nullptr if unused. If GetLineNumberReplacements returns an entry
+  // with has_file=false, this is required.
+  virtual auto GetDefaultFileRE(llvm::ArrayRef<llvm::StringRef> /*filenames*/)
+      -> std::optional<RE2> {
+    return std::nullopt;
+  }
+
   // Returns replacement information for line numbers. See LineReplacement for
   // construction.
-  virtual auto GetLineNumberReplacement(
-      llvm::ArrayRef<llvm::StringRef> filenames) -> LineNumberReplacement;
+  virtual auto GetLineNumberReplacements(
+      llvm::ArrayRef<llvm::StringRef> filenames)
+      -> llvm::SmallVector<LineNumberReplacement>;
 
   // Optionally allows children to provide extra replacements for autoupdate.
   virtual auto DoExtraCheckReplacements(std::string& /*check_line*/) -> void {}
diff --git a/testing/file_test/file_test_base_test.cpp b/testing/file_test/file_test_base_test.cpp
index 7231bc3506f9..8a8270dcf86f 100644
--- a/testing/file_test/file_test_base_test.cpp
+++ b/testing/file_test/file_test_base_test.cpp
@@ -9,12 +9,11 @@
 
 #include "common/ostream.h"
 #include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/FormatVariadic.h"
 
 namespace Carbon::Testing {
 namespace {
 
-using ::testing::Eq;
-
 class FileTestBaseTest : public FileTestBase {
  public:
   using FileTestBase::FileTestBase;
@@ -96,6 +95,27 @@ class FileTestBaseTest : public FileTestBase {
       stderr << "unattached message 3\n"
              << "unattached message 4\n";
       return true;
+    } else if (filename == "file_only_re_one_file.carbon") {
+      stdout << "unattached message 1\n"
+             << "file: file_only_re_one_file.carbon\n"
+             << "line: 1\n"
+             << "unattached message 2\n";
+      return true;
+    } else if (filename == "file_only_re_multi_file.carbon") {
+      int msg_count = 0;
+      stdout << "unattached message " << ++msg_count << "\n"
+             << "file: a.carbon\n"
+             << "unattached message " << ++msg_count << "\n"
+             << "line: 1: attached message " << ++msg_count << "\n"
+             << "unattached message " << ++msg_count << "\n"
+             << "line: 8: late message " << ++msg_count << "\n"
+             << "unattached message " << ++msg_count << "\n"
+             << "file: b.carbon\n"
+             << "line: 1: attached message " << ++msg_count << "\n"
+             << "unattached message " << ++msg_count << "\n"
+             << "line: 7: late message " << ++msg_count << "\n"
+             << "unattached message " << ++msg_count << "\n";
+      return true;
     } else {
       return ErrorBuilder() << "Unexpected file: " << filename;
     }
@@ -104,6 +124,24 @@ class FileTestBaseTest : public FileTestBase {
   auto GetDefaultArgs() -> llvm::SmallVector<std::string> override {
     return {"default_args", "%s"};
   }
+
+  auto GetDefaultFileRE(llvm::ArrayRef<llvm::StringRef> filenames)
+      -> std::optional<RE2> override {
+    return std::make_optional<RE2>(
+        llvm::formatv(R"(file: ({0}))", llvm::join(filenames, "|")));
+  }
+
+  auto GetLineNumberReplacements(llvm::ArrayRef<llvm::StringRef> filenames)
+      -> llvm::SmallVector<LineNumberReplacement> override {
+    auto replacements = FileTestBase::GetLineNumberReplacements(filenames);
+    auto filename = std::filesystem::path(test_name().str()).filename();
+    if (llvm::StringRef(filename).startswith("file_only_re_")) {
+      replacements.push_back({.has_file = false,
+                              .re = std::make_shared<RE2>(R"(line: (\d+))"),
+                              .line_formatv = "{0}"});
+    }
+    return replacements;
+  }
 };
 
 }  // namespace
diff --git a/testing/file_test/testdata/file_only_re_multi_file.carbon b/testing/file_test/testdata/file_only_re_multi_file.carbon
new file mode 100644
index 000000000000..e979b8c8d3d7
--- /dev/null
+++ b/testing/file_test/testdata/file_only_re_multi_file.carbon
@@ -0,0 +1,25 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// AUTOUPDATE
+// CHECK:STDOUT: 3 args: `default_args`, `a.carbon`, `b.carbon`
+// CHECK:STDOUT: unattached message 1
+
+// --- a.carbon
+aaa
+// CHECK:STDOUT: file: a.carbon
+// CHECK:STDOUT: unattached message 2
+// CHECK:STDOUT: line: [[@LINE-3]]: attached message 3
+// CHECK:STDOUT: unattached message 4
+
+// CHECK:STDOUT: line: [[@LINE+1]]: late message 5
+// CHECK:STDOUT: unattached message 6
+// --- b.carbon
+bbb
+// CHECK:STDOUT: file: b.carbon
+// CHECK:STDOUT: line: [[@LINE-2]]: attached message 7
+// CHECK:STDOUT: unattached message 8
+
+// CHECK:STDOUT: line: [[@LINE+1]]: late message 9
+// CHECK:STDOUT: unattached message 10
diff --git a/testing/file_test/testdata/file_only_re_one_file.carbon b/testing/file_test/testdata/file_only_re_one_file.carbon
new file mode 100644
index 000000000000..cd081ca3430b
--- /dev/null
+++ b/testing/file_test/testdata/file_only_re_one_file.carbon
@@ -0,0 +1,10 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+// AUTOUPDATE
+// CHECK:STDOUT: 2 args: `default_args`, `file_only_re_one_file.carbon`
+// CHECK:STDOUT: unattached message 1
+// CHECK:STDOUT: file: file_only_re_one_file.carbon
+// CHECK:STDOUT: line: [[@LINE-8]]
+// CHECK:STDOUT: unattached message 2
diff --git a/testing/file_test/testdata/unattached_multi_file.carbon b/testing/file_test/testdata/unattached_multi_file.carbon
index 7c54423489e3..3366a997a623 100644
--- a/testing/file_test/testdata/unattached_multi_file.carbon
+++ b/testing/file_test/testdata/unattached_multi_file.carbon
@@ -6,12 +6,11 @@
 // CHECK:STDERR: unattached message 3
 // CHECK:STDERR: unattached message 4
 
+// CHECK:STDOUT: 3 args: `default_args`, `a.carbon`, `b.carbon`
+// CHECK:STDOUT: unattached message 1
+// CHECK:STDOUT: unattached message 2
 // --- a.carbon
 aaa
 
 // --- b.carbon
 bbb
-
-// CHECK:STDOUT: 3 args: `default_args`, `a.carbon`, `b.carbon`
-// CHECK:STDOUT: unattached message 1
-// CHECK:STDOUT: unattached message 2
diff --git a/toolchain/autoupdate_testdata.py b/toolchain/autoupdate_testdata.py
index 93c135e2f6d8..6e0b20173b94 100755
--- a/toolchain/autoupdate_testdata.py
+++ b/toolchain/autoupdate_testdata.py
@@ -26,13 +26,13 @@ def main() -> None:
     # Support specifying tests to update, such as:
     # ./autoupdate_testdata.py lex/**/*
     if len(sys.argv) > 1:
-        repo_root = Path(__file__).parent.parent
+        repo_root = Path(__file__).resolve().parent.parent
         file_tests = []
         # Filter down to just test files.
         for f in sys.argv[1:]:
             if f.endswith(".carbon"):
-                path = str(Path(f).absolute().relative_to(repo_root))
-                if path.find("/testdata/"):
+                path = str(Path(f).resolve().relative_to(repo_root))
+                if path.count("/testdata/"):
                     file_tests.append(path)
         if not file_tests:
             sys.exit(
diff --git a/toolchain/driver/driver_test.cpp b/toolchain/driver/driver_test.cpp
index 420b891405eb..e681b694766d 100644
--- a/toolchain/driver/driver_test.cpp
+++ b/toolchain/driver/driver_test.cpp
@@ -15,13 +15,11 @@
 #include "llvm/Object/Binary.h"
 #include "llvm/Support/FormatVariadic.h"
 #include "testing/base/test_raw_ostream.h"
-#include "toolchain/base/yaml_test_helpers.h"
 
 namespace Carbon::Testing {
 namespace {
 
 using ::testing::ContainsRegex;
-using ::testing::ElementsAre;
 using ::testing::HasSubstr;
 using ::testing::StrEq;
 
@@ -126,32 +124,8 @@ TEST_F(DriverTest, DumpTokens) {
   EXPECT_TRUE(
       driver_.RunCommand({"compile", "--phase=lex", "--dump-tokens", file}));
   EXPECT_THAT(test_error_stream_.TakeStr(), StrEq(""));
-  auto tokenized_text = test_output_stream_.TakeStr();
-
-  EXPECT_THAT(Yaml::Value::FromText(tokenized_text),
-              ElementsAre(Yaml::SequenceValue{
-                  Yaml::MappingValue{{"index", "0"},
-                                     {"kind", "Identifier"},
-                                     {"line", "1"},
-                                     {"column", "1"},
-                                     {"indent", "1"},
-                                     {"spelling", "Hello"},
-                                     {"identifier", "0"},
-                                     {"has_trailing_space", "true"}},
-                  Yaml::MappingValue{{"index", "1"},
-                                     {"kind", "Identifier"},
-                                     {"line", "1"},
-                                     {"column", "7"},
-                                     {"indent", "1"},
-                                     {"spelling", "World"},
-                                     {"identifier", "1"},
-                                     {"has_trailing_space", "true"}},
-                  Yaml::MappingValue{{"index", "2"},
-                                     {"kind", "EndOfFile"},
-                                     {"line", "1"},
-                                     {"column", "12"},
-                                     {"indent", "1"},
-                                     {"spelling", ""}}}));
+  // Verify there is output without examining it.
+  EXPECT_FALSE(test_output_stream_.TakeStr().empty());
 }
 
 TEST_F(DriverTest, DumpParseTree) {
diff --git a/toolchain/lex/testdata/basic_syntax.carbon b/toolchain/lex/testdata/basic_syntax.carbon
index 8c46028a1f40..8643fffd84bf 100644
--- a/toolchain/lex/testdata/basic_syntax.carbon
+++ b/toolchain/lex/testdata/basic_syntax.carbon
@@ -3,22 +3,23 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: basic_syntax.carbon
+// CHECK:STDOUT:   tokens: [
 
 fn run(String program) {
-// CHECK:STDOUT: { index:  0, kind:                'Fn', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'fn', has_trailing_space: true },
-// CHECK:STDOUT: { index:  1, kind:        'Identifier', line: {{ *}}[[@LINE-2]], column:  4, indent: 1, spelling: 'run', identifier: 0 },
-// CHECK:STDOUT: { index:  2, kind:         'OpenParen', line: {{ *}}[[@LINE-3]], column:  7, indent: 1, spelling: '(', closing_token: 5 },
-// CHECK:STDOUT: { index:  3, kind: 'StringTypeLiteral', line: {{ *}}[[@LINE-4]], column:  8, indent: 1, spelling: 'String', has_trailing_space: true },
-// CHECK:STDOUT: { index:  4, kind:        'Identifier', line: {{ *}}[[@LINE-5]], column: 15, indent: 1, spelling: 'program', identifier: 1 },
-// CHECK:STDOUT: { index:  5, kind:        'CloseParen', line: {{ *}}[[@LINE-6]], column: 22, indent: 1, spelling: ')', opening_token: 2, has_trailing_space: true },
-// CHECK:STDOUT: { index:  6, kind:    'OpenCurlyBrace', line: {{ *}}[[@LINE-7]], column: 24, indent: 1, spelling: '{', closing_token: 10, has_trailing_space: true },
+// CHECK:STDOUT:     { index:  0, kind:                'Fn', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'fn', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  1, kind:        'Identifier', line: {{ *}}[[@LINE-2]], column:  4, indent: 1, spelling: 'run', identifier: 0 },
+// CHECK:STDOUT:     { index:  2, kind:         'OpenParen', line: {{ *}}[[@LINE-3]], column:  7, indent: 1, spelling: '(', closing_token: 5 },
+// CHECK:STDOUT:     { index:  3, kind: 'StringTypeLiteral', line: {{ *}}[[@LINE-4]], column:  8, indent: 1, spelling: 'String', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  4, kind:        'Identifier', line: {{ *}}[[@LINE-5]], column: 15, indent: 1, spelling: 'program', identifier: 1 },
+// CHECK:STDOUT:     { index:  5, kind:        'CloseParen', line: {{ *}}[[@LINE-6]], column: 22, indent: 1, spelling: ')', opening_token: 2, has_trailing_space: true },
+// CHECK:STDOUT:     { index:  6, kind:    'OpenCurlyBrace', line: {{ *}}[[@LINE-7]], column: 24, indent: 1, spelling: '{', closing_token: 10, has_trailing_space: true },
   return True;
-  // CHECK:STDOUT: { index:  7, kind:            'Return', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: 'return', has_trailing_space: true },
-  // CHECK:STDOUT: { index:  8, kind:        'Identifier', line: {{ *}}[[@LINE-2]], column: 10, indent: 3, spelling: 'True', identifier: 2 },
-  // CHECK:STDOUT: { index:  9, kind:              'Semi', line: {{ *}}[[@LINE-3]], column: 14, indent: 3, spelling: ';', has_trailing_space: true },
+  // CHECK:STDOUT:     { index:  7, kind:            'Return', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: 'return', has_trailing_space: true },
+  // CHECK:STDOUT:     { index:  8, kind:        'Identifier', line: {{ *}}[[@LINE-2]], column: 10, indent: 3, spelling: 'True', identifier: 2 },
+  // CHECK:STDOUT:     { index:  9, kind:              'Semi', line: {{ *}}[[@LINE-3]], column: 14, indent: 3, spelling: ';', has_trailing_space: true },
 }
-// CHECK:STDOUT: { index: 10, kind:   'CloseCurlyBrace', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '}', opening_token: 6, has_trailing_space: true },
+// CHECK:STDOUT:     { index: 10, kind:   'CloseCurlyBrace', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '}', opening_token: 6, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 11, kind:         'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 11, kind:         'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/fail_block_string_second_line.carbon b/toolchain/lex/testdata/fail_block_string_second_line.carbon
index 338c4f95ccf7..c95b7e289def 100644
--- a/toolchain/lex/testdata/fail_block_string_second_line.carbon
+++ b/toolchain/lex/testdata/fail_block_string_second_line.carbon
@@ -4,20 +4,21 @@
 //
 // An autoupdate wants to put the CHECK in the middle of the block string.
 // NOAUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: fail_block_string_second_line.carbon
+// CHECK:STDOUT:   tokens: [
 
 // CHECK:STDERR: fail_block_string_second_line.carbon:[[@LINE+4]]:3: Only whitespace is permitted before the closing `'''` of a multi-line string.
 // CHECK:STDERR:   error here: '''
 // CHECK:STDERR:   ^
 var s: String = '''
   error here: '''
-// CHECK:STDOUT: { index: 0, kind:               'Var', line: {{ *}}[[@LINE-2]], column:  1, indent: 1, spelling: 'var', has_trailing_space: true },
-// CHECK:STDOUT: { index: 1, kind:        'Identifier', line: {{ *}}[[@LINE-3]], column:  5, indent: 1, spelling: 's', identifier: 0 },
-// CHECK:STDOUT: { index: 2, kind:             'Colon', line: {{ *}}[[@LINE-4]], column:  6, indent: 1, spelling: ':', has_trailing_space: true },
-// CHECK:STDOUT: { index: 3, kind: 'StringTypeLiteral', line: {{ *}}[[@LINE-5]], column:  8, indent: 1, spelling: 'String', has_trailing_space: true },
-// CHECK:STDOUT: { index: 4, kind:             'Equal', line: {{ *}}[[@LINE-6]], column: 15, indent: 1, spelling: '=', has_trailing_space: true },
-// CHECK:STDOUT: { index: 5, kind:     'StringLiteral', line: {{ *}}[[@LINE-7]], column: 17, indent: 1, spelling: ''''
+// CHECK:STDOUT:     { index: 0, kind:               'Var', line: {{ *}}[[@LINE-2]], column:  1, indent: 1, spelling: 'var', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 1, kind:        'Identifier', line: {{ *}}[[@LINE-3]], column:  5, indent: 1, spelling: 's', identifier: 0 },
+// CHECK:STDOUT:     { index: 2, kind:             'Colon', line: {{ *}}[[@LINE-4]], column:  6, indent: 1, spelling: ':', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 3, kind: 'StringTypeLiteral', line: {{ *}}[[@LINE-5]], column:  8, indent: 1, spelling: 'String', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 4, kind:             'Equal', line: {{ *}}[[@LINE-6]], column: 15, indent: 1, spelling: '=', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 5, kind:     'StringLiteral', line: {{ *}}[[@LINE-7]], column: 17, indent: 1, spelling: ''''
 // CHECK:STDOUT:   error here: '''', value: `error here: `, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 6, kind:         'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 6, kind:         'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/fail_multifile.carbon b/toolchain/lex/testdata/fail_multifile.carbon
new file mode 100644
index 000000000000..d3870e2737ad
--- /dev/null
+++ b/toolchain/lex/testdata/fail_multifile.carbon
@@ -0,0 +1,28 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// --- a.carbon
+// CHECK:STDERR: a.carbon:[[@LINE+3]]:3: Empty digit sequence in numeric literal.
+// CHECK:STDERR: 1.a
+// CHECK:STDERR:   ^
+1.a
+// CHECK:STDOUT: - filename: a.carbon
+// CHECK:STDOUT:   tokens: [
+// CHECK:STDOUT:     { index: 0, kind:     'Error', line: {{ *}}[[@LINE-3]], column:  1, indent: 1, spelling: '1.a', has_trailing_space: true },
+
+// CHECK:STDOUT:     { index: 1, kind: 'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
+// --- b.carbon
+// CHECK:STDERR: b.carbon:[[@LINE+3]]:3: Empty digit sequence in numeric literal.
+// CHECK:STDERR: 2.b
+// CHECK:STDERR:   ^
+2.b
+// CHECK:STDOUT: - filename: b.carbon
+// CHECK:STDOUT:   tokens: [
+// CHECK:STDOUT:     { index: 0, kind:     'Error', line: {{ *}}[[@LINE-3]], column:  1, indent: 1, spelling: '2.b', has_trailing_space: true },
+
+// CHECK:STDOUT:     { index: 1, kind: 'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/keywords.carbon b/toolchain/lex/testdata/keywords.carbon
index 4ac9c142a034..f12ec5ea8e57 100644
--- a/toolchain/lex/testdata/keywords.carbon
+++ b/toolchain/lex/testdata/keywords.carbon
@@ -3,133 +3,134 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: keywords.carbon
+// CHECK:STDOUT:   tokens: [
 
 abstract
-// CHECK:STDOUT: { index:  0, kind:            'Abstract', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'abstract', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  0, kind:            'Abstract', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'abstract', has_trailing_space: true },
 adapt
-// CHECK:STDOUT: { index:  1, kind:               'Adapt', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'adapt', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  1, kind:               'Adapt', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'adapt', has_trailing_space: true },
 addr
-// CHECK:STDOUT: { index:  2, kind:                'Addr', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'addr', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  2, kind:                'Addr', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'addr', has_trailing_space: true },
 alias
-// CHECK:STDOUT: { index:  3, kind:               'Alias', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'alias', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  3, kind:               'Alias', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'alias', has_trailing_space: true },
 and
-// CHECK:STDOUT: { index:  4, kind:                 'And', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'and', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  4, kind:                 'And', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'and', has_trailing_space: true },
 api
-// CHECK:STDOUT: { index:  5, kind:                 'Api', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'api', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  5, kind:                 'Api', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'api', has_trailing_space: true },
 as
-// CHECK:STDOUT: { index:  6, kind:                  'As', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'as', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  6, kind:                  'As', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'as', has_trailing_space: true },
 auto
-// CHECK:STDOUT: { index:  7, kind:                'Auto', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'auto', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  7, kind:                'Auto', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'auto', has_trailing_space: true },
 base
-// CHECK:STDOUT: { index:  8, kind:                'Base', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'base', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  8, kind:                'Base', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'base', has_trailing_space: true },
 bool
-// CHECK:STDOUT: { index:  9, kind:                'Bool', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'bool', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  9, kind:                'Bool', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'bool', has_trailing_space: true },
 break
-// CHECK:STDOUT: { index: 10, kind:               'Break', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'break', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 10, kind:               'Break', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'break', has_trailing_space: true },
 case
-// CHECK:STDOUT: { index: 11, kind:                'Case', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'case', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 11, kind:                'Case', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'case', has_trailing_space: true },
 choice
-// CHECK:STDOUT: { index: 12, kind:              'Choice', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'choice', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 12, kind:              'Choice', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'choice', has_trailing_space: true },
 class
-// CHECK:STDOUT: { index: 13, kind:               'Class', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'class', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 13, kind:               'Class', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'class', has_trailing_space: true },
 const
-// CHECK:STDOUT: { index: 14, kind:               'Const', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'const', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 14, kind:               'Const', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'const', has_trailing_space: true },
 constraint
-// CHECK:STDOUT: { index: 15, kind:          'Constraint', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'constraint', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 15, kind:          'Constraint', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'constraint', has_trailing_space: true },
 continue
-// CHECK:STDOUT: { index: 16, kind:            'Continue', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'continue', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 16, kind:            'Continue', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'continue', has_trailing_space: true },
 default
-// CHECK:STDOUT: { index: 17, kind:             'Default', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'default', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 17, kind:             'Default', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'default', has_trailing_space: true },
 destructor
-// CHECK:STDOUT: { index: 18, kind:          'Destructor', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'destructor', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 18, kind:          'Destructor', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'destructor', has_trailing_space: true },
 else
-// CHECK:STDOUT: { index: 19, kind:                'Else', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'else', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 19, kind:                'Else', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'else', has_trailing_space: true },
 extend
-// CHECK:STDOUT: { index: 20, kind:              'Extend', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'extend', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 20, kind:              'Extend', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'extend', has_trailing_space: true },
 false
-// CHECK:STDOUT: { index: 21, kind:               'False', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'false', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 21, kind:               'False', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'false', has_trailing_space: true },
 final
-// CHECK:STDOUT: { index: 22, kind:               'Final', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'final', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 22, kind:               'Final', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'final', has_trailing_space: true },
 fn
-// CHECK:STDOUT: { index: 23, kind:                  'Fn', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'fn', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 23, kind:                  'Fn', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'fn', has_trailing_space: true },
 for
-// CHECK:STDOUT: { index: 24, kind:                 'For', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'for', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 24, kind:                 'For', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'for', has_trailing_space: true },
 forall
-// CHECK:STDOUT: { index: 25, kind:              'Forall', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'forall', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 25, kind:              'Forall', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'forall', has_trailing_space: true },
 friend
-// CHECK:STDOUT: { index: 26, kind:              'Friend', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'friend', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 26, kind:              'Friend', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'friend', has_trailing_space: true },
 if
-// CHECK:STDOUT: { index: 27, kind:                  'If', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'if', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 27, kind:                  'If', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'if', has_trailing_space: true },
 impl
-// CHECK:STDOUT: { index: 28, kind:                'Impl', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'impl', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 28, kind:                'Impl', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'impl', has_trailing_space: true },
 impls
-// CHECK:STDOUT: { index: 29, kind:               'Impls', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'impls', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 29, kind:               'Impls', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'impls', has_trailing_space: true },
 import
-// CHECK:STDOUT: { index: 30, kind:              'Import', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'import', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 30, kind:              'Import', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'import', has_trailing_space: true },
 in
-// CHECK:STDOUT: { index: 31, kind:                  'In', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'in', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 31, kind:                  'In', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'in', has_trailing_space: true },
 interface
-// CHECK:STDOUT: { index: 32, kind:           'Interface', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'interface', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 32, kind:           'Interface', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'interface', has_trailing_space: true },
 let
-// CHECK:STDOUT: { index: 33, kind:                 'Let', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'let', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 33, kind:                 'Let', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'let', has_trailing_space: true },
 library
-// CHECK:STDOUT: { index: 34, kind:             'Library', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'library', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 34, kind:             'Library', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'library', has_trailing_space: true },
 like
-// CHECK:STDOUT: { index: 35, kind:                'Like', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'like', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 35, kind:                'Like', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'like', has_trailing_space: true },
 match
-// CHECK:STDOUT: { index: 36, kind:               'Match', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'match', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 36, kind:               'Match', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'match', has_trailing_space: true },
 namespace
-// CHECK:STDOUT: { index: 37, kind:           'Namespace', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'namespace', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 37, kind:           'Namespace', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'namespace', has_trailing_space: true },
 not
-// CHECK:STDOUT: { index: 38, kind:                 'Not', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'not', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 38, kind:                 'Not', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'not', has_trailing_space: true },
 observe
-// CHECK:STDOUT: { index: 39, kind:             'Observe', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'observe', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 39, kind:             'Observe', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'observe', has_trailing_space: true },
 or
-// CHECK:STDOUT: { index: 40, kind:                  'Or', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'or', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 40, kind:                  'Or', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'or', has_trailing_space: true },
 override
-// CHECK:STDOUT: { index: 41, kind:            'Override', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'override', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 41, kind:            'Override', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'override', has_trailing_space: true },
 package
-// CHECK:STDOUT: { index: 42, kind:             'Package', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'package', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 42, kind:             'Package', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'package', has_trailing_space: true },
 partial
-// CHECK:STDOUT: { index: 43, kind:             'Partial', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'partial', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 43, kind:             'Partial', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'partial', has_trailing_space: true },
 private
-// CHECK:STDOUT: { index: 44, kind:             'Private', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'private', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 44, kind:             'Private', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'private', has_trailing_space: true },
 protected
-// CHECK:STDOUT: { index: 45, kind:           'Protected', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'protected', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 45, kind:           'Protected', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'protected', has_trailing_space: true },
 require
-// CHECK:STDOUT: { index: 46, kind:             'Require', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'require', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 46, kind:             'Require', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'require', has_trailing_space: true },
 return
-// CHECK:STDOUT: { index: 47, kind:              'Return', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'return', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 47, kind:              'Return', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'return', has_trailing_space: true },
 returned
-// CHECK:STDOUT: { index: 48, kind:            'Returned', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'returned', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 48, kind:            'Returned', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'returned', has_trailing_space: true },
 Self
-// CHECK:STDOUT: { index: 49, kind:  'SelfTypeIdentifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'Self', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 49, kind:  'SelfTypeIdentifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'Self', has_trailing_space: true },
 self
-// CHECK:STDOUT: { index: 50, kind: 'SelfValueIdentifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'self', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 50, kind: 'SelfValueIdentifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'self', has_trailing_space: true },
 String
-// CHECK:STDOUT: { index: 51, kind:   'StringTypeLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'String', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 51, kind:   'StringTypeLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'String', has_trailing_space: true },
 template
-// CHECK:STDOUT: { index: 52, kind:            'Template', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'template', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 52, kind:            'Template', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'template', has_trailing_space: true },
 then
-// CHECK:STDOUT: { index: 53, kind:                'Then', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'then', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 53, kind:                'Then', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'then', has_trailing_space: true },
 true
-// CHECK:STDOUT: { index: 54, kind:                'True', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'true', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 54, kind:                'True', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'true', has_trailing_space: true },
 type
-// CHECK:STDOUT: { index: 55, kind:                'Type', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'type', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 55, kind:                'Type', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'type', has_trailing_space: true },
 _
-// CHECK:STDOUT: { index: 56, kind:          'Underscore', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '_', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 56, kind:          'Underscore', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '_', has_trailing_space: true },
 var
-// CHECK:STDOUT: { index: 57, kind:                 'Var', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'var', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 57, kind:                 'Var', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'var', has_trailing_space: true },
 virtual
-// CHECK:STDOUT: { index: 58, kind:             'Virtual', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'virtual', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 58, kind:             'Virtual', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'virtual', has_trailing_space: true },
 where
-// CHECK:STDOUT: { index: 59, kind:               'Where', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'where', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 59, kind:               'Where', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'where', has_trailing_space: true },
 while
-// CHECK:STDOUT: { index: 60, kind:               'While', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'while', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 60, kind:               'While', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'while', has_trailing_space: true },
 
 notakeyword
-// CHECK:STDOUT: { index: 61, kind:          'Identifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'notakeyword', identifier: 0, has_trailing_space: true },
+// CHECK:STDOUT:     { index: 61, kind:          'Identifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'notakeyword', identifier: 0, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 62, kind:           'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 62, kind:           'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/multifile.carbon b/toolchain/lex/testdata/multifile.carbon
new file mode 100644
index 000000000000..2afc00084e9f
--- /dev/null
+++ b/toolchain/lex/testdata/multifile.carbon
@@ -0,0 +1,26 @@
+// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+// Exceptions. See /LICENSE for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// AUTOUPDATE
+
+// --- a.carbon
+
+// CHECK:STDOUT: - filename: a.carbon
+// CHECK:STDOUT:   tokens: [
+a;
+// CHECK:STDOUT:     { index: 0, kind: 'Identifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'a', identifier: 0 },
+// CHECK:STDOUT:     { index: 1, kind:       'Semi', line: {{ *}}[[@LINE-2]], column:  2, indent: 1, spelling: ';', has_trailing_space: true },
+
+// CHECK:STDOUT:     { index: 2, kind:  'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
+// --- b.carbon
+
+// CHECK:STDOUT: - filename: b.carbon
+// CHECK:STDOUT:   tokens: [
+b;
+// CHECK:STDOUT:     { index: 0, kind: 'Identifier', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'b', identifier: 0 },
+// CHECK:STDOUT:     { index: 1, kind:       'Semi', line: {{ *}}[[@LINE-2]], column:  2, indent: 1, spelling: ';', has_trailing_space: true },
+
+// CHECK:STDOUT:     { index: 2, kind:  'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/numeric_literals.carbon b/toolchain/lex/testdata/numeric_literals.carbon
index 97899466487d..a8d567b6d702 100644
--- a/toolchain/lex/testdata/numeric_literals.carbon
+++ b/toolchain/lex/testdata/numeric_literals.carbon
@@ -3,82 +3,83 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: numeric_literals.carbon
+// CHECK:STDOUT:   tokens: [
 
 fn F() {
-// CHECK:STDOUT: { index:  0, kind:                       'Fn', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'fn', has_trailing_space: true },
-// CHECK:STDOUT: { index:  1, kind:               'Identifier', line: {{ *}}[[@LINE-2]], column:  4, indent: 1, spelling: 'F', identifier: 0 },
-// CHECK:STDOUT: { index:  2, kind:                'OpenParen', line: {{ *}}[[@LINE-3]], column:  5, indent: 1, spelling: '(', closing_token: 3 },
-// CHECK:STDOUT: { index:  3, kind:               'CloseParen', line: {{ *}}[[@LINE-4]], column:  6, indent: 1, spelling: ')', opening_token: 2, has_trailing_space: true },
-// CHECK:STDOUT: { index:  4, kind:           'OpenCurlyBrace', line: {{ *}}[[@LINE-5]], column:  8, indent: 1, spelling: '{', closing_token: 53, has_trailing_space: true },
+// CHECK:STDOUT:     { index:  0, kind:                       'Fn', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: 'fn', has_trailing_space: true },
+// CHECK:STDOUT:     { index:  1, kind:               'Identifier', line: {{ *}}[[@LINE-2]], column:  4, indent: 1, spelling: 'F', identifier: 0 },
+// CHECK:STDOUT:     { index:  2, kind:                'OpenParen', line: {{ *}}[[@LINE-3]], column:  5, indent: 1, spelling: '(', closing_token: 3 },
+// CHECK:STDOUT:     { index:  3, kind:               'CloseParen', line: {{ *}}[[@LINE-4]], column:  6, indent: 1, spelling: ')', opening_token: 2, has_trailing_space: true },
+// CHECK:STDOUT:     { index:  4, kind:           'OpenCurlyBrace', line: {{ *}}[[@LINE-5]], column:  8, indent: 1, spelling: '{', closing_token: 53, has_trailing_space: true },
   // 8 and 9 trigger special behavior in APInt when mishandling signed versus
   // unsigned, so we pay extra attention to those.
   var ints: [i32; 5] = (
-  // CHECK:STDOUT: { index:  5, kind:                      'Var', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: 'var', has_trailing_space: true },
-  // CHECK:STDOUT: { index:  6, kind:               'Identifier', line: {{ *}}[[@LINE-2]], column:  7, indent: 3, spelling: 'ints', identifier: 1 },
-  // CHECK:STDOUT: { index:  7, kind:                    'Colon', line: {{ *}}[[@LINE-3]], column: 11, indent: 3, spelling: ':', has_trailing_space: true },
-  // CHECK:STDOUT: { index:  8, kind:        'OpenSquareBracket', line: {{ *}}[[@LINE-4]], column: 13, indent: 3, spelling: '[', closing_token: 12 },
-  // CHECK:STDOUT: { index:  9, kind:       'IntegerTypeLiteral', line: {{ *}}[[@LINE-5]], column: 14, indent: 3, spelling: 'i32' },
-  // CHECK:STDOUT: { index: 10, kind:                     'Semi', line: {{ *}}[[@LINE-6]], column: 17, indent: 3, spelling: ';', has_trailing_space: true },
-  // CHECK:STDOUT: { index: 11, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-7]], column: 19, indent: 3, spelling: '5', value: `5` },
-  // CHECK:STDOUT: { index: 12, kind:       'CloseSquareBracket', line: {{ *}}[[@LINE-8]], column: 20, indent: 3, spelling: ']', opening_token: 8, has_trailing_space: true },
-  // CHECK:STDOUT: { index: 13, kind:                    'Equal', line: {{ *}}[[@LINE-9]], column: 22, indent: 3, spelling: '=', has_trailing_space: true },
-  // CHECK:STDOUT: { index: 14, kind:                'OpenParen', line: {{ *}}[[@LINE-10]], column: 24, indent: 3, spelling: '(', closing_token: 25, has_trailing_space: true },
+  // CHECK:STDOUT:     { index:  5, kind:                      'Var', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: 'var', has_trailing_space: true },
+  // CHECK:STDOUT:     { index:  6, kind:               'Identifier', line: {{ *}}[[@LINE-2]], column:  7, indent: 3, spelling: 'ints', identifier: 1 },
+  // CHECK:STDOUT:     { index:  7, kind:                    'Colon', line: {{ *}}[[@LINE-3]], column: 11, indent: 3, spelling: ':', has_trailing_space: true },
+  // CHECK:STDOUT:     { index:  8, kind:        'OpenSquareBracket', line: {{ *}}[[@LINE-4]], column: 13, indent: 3, spelling: '[', closing_token: 12 },
+  // CHECK:STDOUT:     { index:  9, kind:       'IntegerTypeLiteral', line: {{ *}}[[@LINE-5]], column: 14, indent: 3, spelling: 'i32' },
+  // CHECK:STDOUT:     { index: 10, kind:                     'Semi', line: {{ *}}[[@LINE-6]], column: 17, indent: 3, spelling: ';', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 11, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-7]], column: 19, indent: 3, spelling: '5', value: `5` },
+  // CHECK:STDOUT:     { index: 12, kind:       'CloseSquareBracket', line: {{ *}}[[@LINE-8]], column: 20, indent: 3, spelling: ']', opening_token: 8, has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 13, kind:                    'Equal', line: {{ *}}[[@LINE-9]], column: 22, indent: 3, spelling: '=', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 14, kind:                'OpenParen', line: {{ *}}[[@LINE-10]], column: 24, indent: 3, spelling: '(', closing_token: 25, has_trailing_space: true },
     8,
-    // CHECK:STDOUT: { index: 15, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '8', value: `8` },
-    // CHECK:STDOUT: { index: 16, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  6, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 15, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '8', value: `8` },
+    // CHECK:STDOUT:     { index: 16, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  6, indent: 5, spelling: ',', has_trailing_space: true },
     9,
-    // CHECK:STDOUT: { index: 17, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '9', value: `9` },
-    // CHECK:STDOUT: { index: 18, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  6, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 17, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '9', value: `9` },
+    // CHECK:STDOUT:     { index: 18, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  6, indent: 5, spelling: ',', has_trailing_space: true },
     0x8,
-    // CHECK:STDOUT: { index: 19, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '0x8', value: `8` },
-    // CHECK:STDOUT: { index: 20, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  8, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 19, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '0x8', value: `8` },
+    // CHECK:STDOUT:     { index: 20, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  8, indent: 5, spelling: ',', has_trailing_space: true },
     0b1000,
-    // CHECK:STDOUT: { index: 21, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '0b1000', value: `8` },
-    // CHECK:STDOUT: { index: 22, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 11, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 21, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '0b1000', value: `8` },
+    // CHECK:STDOUT:     { index: 22, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 11, indent: 5, spelling: ',', has_trailing_space: true },
     39999999999999999993,
-    // CHECK:STDOUT: { index: 23, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '39999999999999999993', value: `39999999999999999993` },
-    // CHECK:STDOUT: { index: 24, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 25, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 23, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '39999999999999999993', value: `39999999999999999993` },
+    // CHECK:STDOUT:     { index: 24, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 25, indent: 5, spelling: ',', has_trailing_space: true },
   );
-  // CHECK:STDOUT: { index: 25, kind:               'CloseParen', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: ')', opening_token: 14 },
-  // CHECK:STDOUT: { index: 26, kind:                     'Semi', line: {{ *}}[[@LINE-2]], column:  4, indent: 3, spelling: ';', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 25, kind:               'CloseParen', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: ')', opening_token: 14 },
+  // CHECK:STDOUT:     { index: 26, kind:                     'Semi', line: {{ *}}[[@LINE-2]], column:  4, indent: 3, spelling: ';', has_trailing_space: true },
   var floats: [f64; 7] = (
-  // CHECK:STDOUT: { index: 27, kind:                      'Var', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: 'var', has_trailing_space: true },
-  // CHECK:STDOUT: { index: 28, kind:               'Identifier', line: {{ *}}[[@LINE-2]], column:  7, indent: 3, spelling: 'floats', identifier: 2 },
-  // CHECK:STDOUT: { index: 29, kind:                    'Colon', line: {{ *}}[[@LINE-3]], column: 13, indent: 3, spelling: ':', has_trailing_space: true },
-  // CHECK:STDOUT: { index: 30, kind:        'OpenSquareBracket', line: {{ *}}[[@LINE-4]], column: 15, indent: 3, spelling: '[', closing_token: 34 },
-  // CHECK:STDOUT: { index: 31, kind: 'FloatingPointTypeLiteral', line: {{ *}}[[@LINE-5]], column: 16, indent: 3, spelling: 'f64' },
-  // CHECK:STDOUT: { index: 32, kind:                     'Semi', line: {{ *}}[[@LINE-6]], column: 19, indent: 3, spelling: ';', has_trailing_space: true },
-  // CHECK:STDOUT: { index: 33, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-7]], column: 21, indent: 3, spelling: '7', value: `7` },
-  // CHECK:STDOUT: { index: 34, kind:       'CloseSquareBracket', line: {{ *}}[[@LINE-8]], column: 22, indent: 3, spelling: ']', opening_token: 30, has_trailing_space: true },
-  // CHECK:STDOUT: { index: 35, kind:                    'Equal', line: {{ *}}[[@LINE-9]], column: 24, indent: 3, spelling: '=', has_trailing_space: true },
-  // CHECK:STDOUT: { index: 36, kind:                'OpenParen', line: {{ *}}[[@LINE-10]], column: 26, indent: 3, spelling: '(', closing_token: 51, has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 27, kind:                      'Var', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: 'var', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 28, kind:               'Identifier', line: {{ *}}[[@LINE-2]], column:  7, indent: 3, spelling: 'floats', identifier: 2 },
+  // CHECK:STDOUT:     { index: 29, kind:                    'Colon', line: {{ *}}[[@LINE-3]], column: 13, indent: 3, spelling: ':', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 30, kind:        'OpenSquareBracket', line: {{ *}}[[@LINE-4]], column: 15, indent: 3, spelling: '[', closing_token: 34 },
+  // CHECK:STDOUT:     { index: 31, kind: 'FloatingPointTypeLiteral', line: {{ *}}[[@LINE-5]], column: 16, indent: 3, spelling: 'f64' },
+  // CHECK:STDOUT:     { index: 32, kind:                     'Semi', line: {{ *}}[[@LINE-6]], column: 19, indent: 3, spelling: ';', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 33, kind:           'IntegerLiteral', line: {{ *}}[[@LINE-7]], column: 21, indent: 3, spelling: '7', value: `7` },
+  // CHECK:STDOUT:     { index: 34, kind:       'CloseSquareBracket', line: {{ *}}[[@LINE-8]], column: 22, indent: 3, spelling: ']', opening_token: 30, has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 35, kind:                    'Equal', line: {{ *}}[[@LINE-9]], column: 24, indent: 3, spelling: '=', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 36, kind:                'OpenParen', line: {{ *}}[[@LINE-10]], column: 26, indent: 3, spelling: '(', closing_token: 51, has_trailing_space: true },
     0.9,
-    // CHECK:STDOUT: { index: 37, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '0.9', value: `9*10^-1` },
-    // CHECK:STDOUT: { index: 38, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  8, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 37, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '0.9', value: `9*10^-1` },
+    // CHECK:STDOUT:     { index: 38, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  8, indent: 5, spelling: ',', has_trailing_space: true },
     8.0,
-    // CHECK:STDOUT: { index: 39, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '8.0', value: `80*10^-1` },
-    // CHECK:STDOUT: { index: 40, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  8, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 39, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '8.0', value: `80*10^-1` },
+    // CHECK:STDOUT:     { index: 40, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  8, indent: 5, spelling: ',', has_trailing_space: true },
     80.0,
-    // CHECK:STDOUT: { index: 41, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '80.0', value: `800*10^-1` },
-    // CHECK:STDOUT: { index: 42, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  9, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 41, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '80.0', value: `800*10^-1` },
+    // CHECK:STDOUT:     { index: 42, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column:  9, indent: 5, spelling: ',', has_trailing_space: true },
     1.0e7,
-    // CHECK:STDOUT: { index: 43, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '1.0e7', value: `10*10^6` },
-    // CHECK:STDOUT: { index: 44, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 10, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 43, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '1.0e7', value: `10*10^6` },
+    // CHECK:STDOUT:     { index: 44, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 10, indent: 5, spelling: ',', has_trailing_space: true },
     1.0e8,
-    // CHECK:STDOUT: { index: 45, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '1.0e8', value: `10*10^7` },
-    // CHECK:STDOUT: { index: 46, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 10, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 45, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '1.0e8', value: `10*10^7` },
+    // CHECK:STDOUT:     { index: 46, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 10, indent: 5, spelling: ',', has_trailing_space: true },
     1.0e-8,
-    // CHECK:STDOUT: { index: 47, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '1.0e-8', value: `10*10^-9` },
-    // CHECK:STDOUT: { index: 48, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 11, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 47, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '1.0e-8', value: `10*10^-9` },
+    // CHECK:STDOUT:     { index: 48, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 11, indent: 5, spelling: ',', has_trailing_space: true },
     39999999999999999993.0e39999999999999999993,
-    // CHECK:STDOUT: { index: 49, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '39999999999999999993.0e39999999999999999993', value: `399999999999999999930*10^39999999999999999992` },
-    // CHECK:STDOUT: { index: 50, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 48, indent: 5, spelling: ',', has_trailing_space: true },
+    // CHECK:STDOUT:     { index: 49, kind:              'RealLiteral', line: {{ *}}[[@LINE-1]], column:  5, indent: 5, spelling: '39999999999999999993.0e39999999999999999993', value: `399999999999999999930*10^39999999999999999992` },
+    // CHECK:STDOUT:     { index: 50, kind:                    'Comma', line: {{ *}}[[@LINE-2]], column: 48, indent: 5, spelling: ',', has_trailing_space: true },
   );
-  // CHECK:STDOUT: { index: 51, kind:               'CloseParen', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: ')', opening_token: 36 },
-  // CHECK:STDOUT: { index: 52, kind:                     'Semi', line: {{ *}}[[@LINE-2]], column:  4, indent: 3, spelling: ';', has_trailing_space: true },
+  // CHECK:STDOUT:     { index: 51, kind:               'CloseParen', line: {{ *}}[[@LINE-1]], column:  3, indent: 3, spelling: ')', opening_token: 36 },
+  // CHECK:STDOUT:     { index: 52, kind:                     'Semi', line: {{ *}}[[@LINE-2]], column:  4, indent: 3, spelling: ';', has_trailing_space: true },
 }
-// CHECK:STDOUT: { index: 53, kind:          'CloseCurlyBrace', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '}', opening_token: 4, has_trailing_space: true },
+// CHECK:STDOUT:     { index: 53, kind:          'CloseCurlyBrace', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '}', opening_token: 4, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 54, kind:                'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 54, kind:                'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/printing_digit_padding.carbon b/toolchain/lex/testdata/printing_digit_padding.carbon
index 02b198a5506c..c3fa210458d4 100644
--- a/toolchain/lex/testdata/printing_digit_padding.carbon
+++ b/toolchain/lex/testdata/printing_digit_padding.carbon
@@ -3,16 +3,17 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: printing_digit_padding.carbon
+// CHECK:STDOUT:   tokens: [
 
 ;
-// CHECK:STDOUT: { index: 0, kind:      'Semi', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: ';', has_trailing_space: true },
+// CHECK:STDOUT:     { index: 0, kind:      'Semi', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: ';', has_trailing_space: true },
 
 // Test digit padding with values of 9, 10, and 11.
         ;;;
-        // CHECK:STDOUT: { index: 1, kind:      'Semi', line: {{ *}}[[@LINE-1]], column:  9, indent: 9, spelling: ';' },
-        // CHECK:STDOUT: { index: 2, kind:      'Semi', line: {{ *}}[[@LINE-2]], column: 10, indent: 9, spelling: ';' },
-        // CHECK:STDOUT: { index: 3, kind:      'Semi', line: {{ *}}[[@LINE-3]], column: 11, indent: 9, spelling: ';', has_trailing_space: true },
+        // CHECK:STDOUT:     { index: 1, kind:      'Semi', line: {{ *}}[[@LINE-1]], column:  9, indent: 9, spelling: ';' },
+        // CHECK:STDOUT:     { index: 2, kind:      'Semi', line: {{ *}}[[@LINE-2]], column: 10, indent: 9, spelling: ';' },
+        // CHECK:STDOUT:     { index: 3, kind:      'Semi', line: {{ *}}[[@LINE-3]], column: 11, indent: 9, spelling: ';', has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 4, kind: 'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 4, kind: 'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/printing_integer_literal.carbon b/toolchain/lex/testdata/printing_integer_literal.carbon
index dfc56e15fd09..b0da32c83d8d 100644
--- a/toolchain/lex/testdata/printing_integer_literal.carbon
+++ b/toolchain/lex/testdata/printing_integer_literal.carbon
@@ -3,10 +3,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: printing_integer_literal.carbon
+// CHECK:STDOUT:   tokens: [
 
 123
-// CHECK:STDOUT: { index: 0, kind: 'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '123', value: `123`, has_trailing_space: true },
+// CHECK:STDOUT:     { index: 0, kind: 'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '123', value: `123`, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 1, kind:      'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 1, kind:      'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/printing_real_literal.carbon b/toolchain/lex/testdata/printing_real_literal.carbon
index 75350459cb03..4f1bcfb39cdf 100644
--- a/toolchain/lex/testdata/printing_real_literal.carbon
+++ b/toolchain/lex/testdata/printing_real_literal.carbon
@@ -3,10 +3,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: printing_real_literal.carbon
+// CHECK:STDOUT:   tokens: [
 
 2.5
-// CHECK:STDOUT: { index: 0, kind: 'RealLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '2.5', value: `25*10^-1`, has_trailing_space: true },
+// CHECK:STDOUT:     { index: 0, kind: 'RealLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '2.5', value: `25*10^-1`, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 1, kind:   'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 1, kind:   'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/testdata/printing_token.carbon b/toolchain/lex/testdata/printing_token.carbon
index 923c4fe7b77d..8ab728a490de 100644
--- a/toolchain/lex/testdata/printing_token.carbon
+++ b/toolchain/lex/testdata/printing_token.carbon
@@ -3,10 +3,11 @@
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 // AUTOUPDATE
-// CHECK:STDOUT: [
+// CHECK:STDOUT: - filename: printing_token.carbon
+// CHECK:STDOUT:   tokens: [
 
 0x9
-// CHECK:STDOUT: { index: 0, kind: 'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '0x9', value: `9`, has_trailing_space: true },
+// CHECK:STDOUT:     { index: 0, kind: 'IntegerLiteral', line: {{ *}}[[@LINE-1]], column:  1, indent: 1, spelling: '0x9', value: `9`, has_trailing_space: true },
 
-// CHECK:STDOUT: { index: 1, kind:      'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
-// CHECK:STDOUT: ]
+// CHECK:STDOUT:     { index: 1, kind:      'EndOfFile', line: {{ *}}[[@LINE+1]], column: {{ *\d+}}, indent: 1, spelling: '' },
+// CHECK:STDOUT:   ]
diff --git a/toolchain/lex/tokenized_buffer.cpp b/toolchain/lex/tokenized_buffer.cpp
index 880761c1473c..3bc12f17b816 100644
--- a/toolchain/lex/tokenized_buffer.cpp
+++ b/toolchain/lex/tokenized_buffer.cpp
@@ -1045,18 +1045,20 @@ auto TokenizedBuffer::Print(llvm::raw_ostream& output_stream) const -> void {
     return;
   }
 
+  output_stream << "- filename: " << source_->filename() << "\n"
+                << "  tokens: [\n";
+
   PrintWidths widths = {};
   widths.index = ComputeDecimalPrintedWidth((token_infos_.size()));
   for (Token token : tokens()) {
     widths.Widen(GetTokenPrintWidths(token));
   }
 
-  output_stream << "[\n";
   for (Token token : tokens()) {
     PrintToken(output_stream, token, widths);
     output_stream << "\n";
   }
-  output_stream << "]\n";
+  output_stream << "  ]\n";
 }
 
 auto TokenizedBuffer::PrintToken(llvm::raw_ostream& output_stream,
@@ -1075,7 +1077,7 @@ auto TokenizedBuffer::PrintToken(llvm::raw_ostream& output_stream, Token token,
   // justification manually in order to use the dynamically computed widths
   // and get the quotes included.
   output_stream << llvm::formatv(
-      "{ index: {0}, kind: {1}, line: {2}, column: {3}, indent: {4}, "
+      "    { index: {0}, kind: {1}, line: {2}, column: {3}, indent: {4}, "
       "spelling: '{5}'",
       llvm::format_decimal(token_index, widths.index),
       llvm::right_justify(llvm::formatv("'{0}'", token_info.kind.name()).str(),
diff --git a/toolchain/lex/tokenized_buffer_test.cpp b/toolchain/lex/tokenized_buffer_test.cpp
index 6300e1d5daa9..e32e467b5ffc 100644
--- a/toolchain/lex/tokenized_buffer_test.cpp
+++ b/toolchain/lex/tokenized_buffer_test.cpp
@@ -1001,35 +1001,38 @@ TEST_F(LexerTest, PrintingAsYaml) {
   TestRawOstream print_stream;
   buffer.Print(print_stream);
 
-  EXPECT_THAT(Yaml::Value::FromText(print_stream.TakeStr()),
-              ElementsAre(Yaml::SequenceValue{
-                  Yaml::MappingValue{{"index", "0"},
-                                     {"kind", "Semi"},
-                                     {"line", "2"},
-                                     {"column", "2"},
-                                     {"indent", "2"},
-                                     {"spelling", ";"},
-                                     {"has_trailing_space", "true"}},
-                  Yaml::MappingValue{{"index", "1"},
-                                     {"kind", "Semi"},
-                                     {"line", "5"},
-                                     {"column", "1"},
-                                     {"indent", "1"},
-                                     {"spelling", ";"},
-                                     {"has_trailing_space", "true"}},
-                  Yaml::MappingValue{{"index", "2"},
-                                     {"kind", "Semi"},
-                                     {"line", "5"},
-                                     {"column", "3"},
-                                     {"indent", "1"},
-                                     {"spelling", ";"},
-                                     {"has_trailing_space", "true"}},
-                  Yaml::MappingValue{{"index", "3"},
-                                     {"kind", "EndOfFile"},
-                                     {"line", "15"},
-                                     {"column", "1"},
-                                     {"indent", "1"},
-                                     {"spelling", ""}}}));
+  EXPECT_THAT(
+      Yaml::Value::FromText(print_stream.TakeStr()),
+      ElementsAre(Yaml::SequenceValue{Yaml::MappingValue{
+          {"filename", Yaml::ScalarValue{source_storage_.front().filename()}},
+          {"tokens", Yaml::SequenceValue{
+                         Yaml::MappingValue{{"index", "0"},
+                                            {"kind", "Semi"},
+                                            {"line", "2"},
+                                            {"column", "2"},
+                                            {"indent", "2"},
+                                            {"spelling", ";"},
+                                            {"has_trailing_space", "true"}},
+                         Yaml::MappingValue{{"index", "1"},
+                                            {"kind", "Semi"},
+                                            {"line", "5"},
+                                            {"column", "1"},
+                                            {"indent", "1"},
+                                            {"spelling", ";"},
+                                            {"has_trailing_space", "true"}},
+                         Yaml::MappingValue{{"index", "2"},
+                                            {"kind", "Semi"},
+                                            {"line", "5"},
+                                            {"column", "3"},
+                                            {"indent", "1"},
+                                            {"spelling", ";"},
+                                            {"has_trailing_space", "true"}},
+                         Yaml::MappingValue{{"index", "3"},
+                                            {"kind", "EndOfFile"},
+                                            {"line", "15"},
+                                            {"column", "1"},
+                                            {"indent", "1"},
+                                            {"spelling", ""}}}}}}));
 }
 
 }  // namespace
diff --git a/toolchain/testing/file_test.cpp b/toolchain/testing/file_test.cpp
index e3f65d64e7fd..696d22387ece 100644
--- a/toolchain/testing/file_test.cpp
+++ b/toolchain/testing/file_test.cpp
@@ -9,6 +9,7 @@
 
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/FormatVariadic.h"
 #include "llvm/Support/VirtualFileSystem.h"
 #include "testing/file_test/file_test_base.h"
 #include "toolchain/driver/driver.h"
@@ -47,16 +48,25 @@ class ToolchainFileTest : public FileTestBase {
     }
   }
 
-  auto GetLineNumberReplacement(llvm::ArrayRef<llvm::StringRef> filenames)
-      -> LineNumberReplacement override {
+  auto GetDefaultFileRE(llvm::ArrayRef<llvm::StringRef> filenames)
+      -> std::optional<RE2> override {
     if (component_ == "lex") {
-      return {.has_file = false,
-              .pattern = R"(line: (\s*\d+))",
-              // The `{{{{` becomes `{{`.
-              .line_formatv = "{{{{ *}}{0}"};
-    } else {
-      return FileTestBase::GetLineNumberReplacement(filenames);
+      return std::make_optional<RE2>(
+          llvm::formatv(R"(^- filename: ({0})$)", llvm::join(filenames, "|")));
     }
+    return FileTestBase::GetDefaultFileRE(filenames);
+  }
+
+  auto GetLineNumberReplacements(llvm::ArrayRef<llvm::StringRef> filenames)
+      -> llvm::SmallVector<LineNumberReplacement> override {
+    auto replacements = FileTestBase::GetLineNumberReplacements(filenames);
+    if (component_ == "lex") {
+      replacements.push_back({.has_file = false,
+                              .re = std::make_shared<RE2>(R"(line: (\s*\d+))"),
+                              // The `{{{{` becomes `{{`.
+                              .line_formatv = "{{{{ *}}{0}"});
+    }
+    return replacements;
   }
 
   auto DoExtraCheckReplacements(std::string& check_line) -> void override {