Rename //explorer/common to base (#3103)

Renaming per #3100

explorer/base/decompose_test.cpp

@@ -0,0 +1,39 @@
+// 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
+
+#include "explorer/base/decompose.h"
+
+#include <gtest/gtest.h>
+
+namespace Carbon {
+namespace {
+
+struct Decomposeable : public HashFromDecompose<Decomposeable> {
+  template <typename F>
+  auto Decompose(F f) const {
+    return f(i, s);
+  }
+
+  int i = 0;
+  std::string s;
+};
+
+TEST(HashFromDecomposeTest, EqualValues) {
+  Decomposeable d1 = {.i = 42, .s = "foo"};
+  Decomposeable d2 = {.i = 42, .s = "foo"};
+
+  EXPECT_TRUE(d1 == d2);
+  EXPECT_TRUE(hash_value(d1) == hash_value(d2));
+}
+
+TEST(HashFromDecomposeTest, NonEqualValues) {
+  Decomposeable d1 = {.i = 42, .s = "foo"};
+  Decomposeable d2 = {.i = 42, .s = "bar"};
+
+  EXPECT_FALSE(d1 == d2);
+  EXPECT_FALSE(hash_value(d1) == hash_value(d2));
+}
+
+}  // namespace
+}  // namespace Carbon