diff --git a/toolchain/check/context.cpp b/toolchain/check/context.cpp
index ecdfdb937951..dad4799c11a0 100644
--- a/toolchain/check/context.cpp
+++ b/toolchain/check/context.cpp
@@ -493,9 +493,6 @@ auto Context::LookupQualifiedName(SemIRLoc loc, SemIR::NameId name_id,
 
     // If this is our second lookup result, diagnose an ambiguity.
     if (result.inst_id.is_valid()) {
-      // TODO: This is currently not reachable because the only scope that can
-      // extend is a class scope, and it can only extend a single base class.
-      // Add test coverage once this is possible.
       CARBON_DIAGNOSTIC(
           NameAmbiguousDueToExtend, Error,
           "ambiguous use of name `{0}` found in multiple extended scopes",
diff --git a/toolchain/check/testdata/impl/multiple_extend.carbon b/toolchain/check/testdata/impl/multiple_extend.carbon
new file mode 100644
index 000000000000..67433e957bfd
--- /dev/null
+++ b/toolchain/check/testdata/impl/multiple_extend.carbon
@@ -0,0 +1,940 @@
+// 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
+// TIP: To test this file alone, run:
+// TIP:   bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/check/testdata/impl/multiple_extend.carbon
+// TIP: To dump output, run:
+// TIP:   bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/check/testdata/impl/multiple_extend.carbon
+
+// --- different_impl_member_names.carbon
+
+library "[[@TEST_NAME]]";
+
+interface HasF {
+  fn F();
+}
+
+interface HasG {
+  fn G();
+}
+
+class C {
+  extend impl as HasF {
+    fn F() {}
+  }
+  extend impl as HasG {
+    fn G() {}
+  }
+}
+
+fn H(c: C) {
+  C.F();
+  c.F();
+  C.G();
+  c.G();
+}
+
+// --- fail_ambiguous_impls.carbon
+
+library "[[@TEST_NAME]]";
+
+interface HasA1 {
+  fn A();
+}
+
+interface HasA2 {
+  fn A();
+}
+
+class D {
+  extend impl as HasA1 {
+    fn A() {}
+  }
+  extend impl as HasA2 {
+    fn A() {}
+  }
+}
+
+fn B(d: D) {
+  // CHECK:STDERR: fail_ambiguous_impls.carbon:[[@LINE+4]]:3: error: ambiguous use of name `A` found in multiple extended scopes [NameAmbiguousDueToExtend]
+  // CHECK:STDERR:   D.A();
+  // CHECK:STDERR:   ^~~
+  // CHECK:STDERR:
+  D.A();
+  // CHECK:STDERR: fail_ambiguous_impls.carbon:[[@LINE+4]]:3: error: ambiguous use of name `A` found in multiple extended scopes [NameAmbiguousDueToExtend]
+  // CHECK:STDERR:   d.A();
+  // CHECK:STDERR:   ^~~
+  // CHECK:STDERR:
+  d.A();
+}
+
+// --- different_impl_and_base.carbon
+
+library "[[@TEST_NAME]]";
+
+interface HasI {
+  fn I();
+}
+
+base class B {
+  fn J() {}
+}
+
+class E {
+  extend base: B;
+  extend impl as HasI {
+    fn I() {}
+  }
+}
+
+fn H(e: E) {
+  E.I();
+  e.I();
+  E.J();
+  e.J();
+}
+
+// --- fail_ambiguous_impl_and_base.carbon
+
+library "[[@TEST_NAME]]";
+
+base class Base {
+  fn K() {}
+}
+
+interface HasK {
+  fn K();
+}
+
+class L {
+  extend base: Base;
+  extend impl as HasK {
+    fn K() {}
+  }
+}
+
+fn M(l: L) {
+   // CHECK:STDERR: fail_ambiguous_impl_and_base.carbon:[[@LINE+4]]:4: error: ambiguous use of name `K` found in multiple extended scopes [NameAmbiguousDueToExtend]
+   // CHECK:STDERR:    L.K();
+   // CHECK:STDERR:    ^~~
+   // CHECK:STDERR:
+   L.K();
+   // CHECK:STDERR: fail_ambiguous_impl_and_base.carbon:[[@LINE+3]]:4: error: ambiguous use of name `K` found in multiple extended scopes [NameAmbiguousDueToExtend]
+   // CHECK:STDERR:    l.K();
+   // CHECK:STDERR:    ^~~
+   l.K();
+}
+
+// --- ambiguity_hidden.carbon
+
+library "[[@TEST_NAME]]";
+
+base class NBase {
+  fn N() {}
+}
+
+interface HasN1 {
+  fn N();
+}
+
+interface HasN2 {
+  fn N();
+}
+
+class O {
+  extend base: NBase;
+  extend impl as HasN1 {
+    fn N() {}
+  }
+  extend impl as HasN2 {
+    fn N() {}
+  }
+  fn N();
+}
+
+fn P(o: O) {
+   O.N();
+   o.N();
+}
+
+// CHECK:STDOUT: --- different_impl_member_names.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %HasF.type: type = interface_type @HasF [template]
+// CHECK:STDOUT:   %Self.1: %HasF.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %F.type.1: type = fn_type @F.1 [template]
+// CHECK:STDOUT:   %.1: type = tuple_type () [template]
+// CHECK:STDOUT:   %F.1: %F.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.2: type = assoc_entity_type %HasF.type, %F.type.1 [template]
+// CHECK:STDOUT:   %.3: %.2 = assoc_entity element0, @HasF.%F.decl [template]
+// CHECK:STDOUT:   %HasG.type: type = interface_type @HasG [template]
+// CHECK:STDOUT:   %Self.2: %HasG.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %G.type.1: type = fn_type @G.1 [template]
+// CHECK:STDOUT:   %G.1: %G.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.4: type = assoc_entity_type %HasG.type, %G.type.1 [template]
+// CHECK:STDOUT:   %.5: %.4 = assoc_entity element0, @HasG.%G.decl [template]
+// CHECK:STDOUT:   %C: type = class_type @C [template]
+// CHECK:STDOUT:   %F.type.2: type = fn_type @F.2 [template]
+// CHECK:STDOUT:   %F.2: %F.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.6: <witness> = interface_witness (%F.2) [template]
+// CHECK:STDOUT:   %G.type.2: type = fn_type @G.2 [template]
+// CHECK:STDOUT:   %G.2: %G.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.7: <witness> = interface_witness (%G.2) [template]
+// CHECK:STDOUT:   %.8: type = struct_type {} [template]
+// CHECK:STDOUT:   %.9: <witness> = complete_type_witness %.8 [template]
+// CHECK:STDOUT:   %H.type: type = fn_type @H [template]
+// CHECK:STDOUT:   %H: %H.type = struct_value () [template]
+// CHECK:STDOUT:   %.10: type = ptr_type %.8 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .HasF = %HasF.decl
+// CHECK:STDOUT:     .HasG = %HasG.decl
+// CHECK:STDOUT:     .C = %C.decl
+// CHECK:STDOUT:     .H = %H.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %HasF.decl: type = interface_decl @HasF [template = constants.%HasF.type] {} {}
+// CHECK:STDOUT:   %HasG.decl: type = interface_decl @HasG [template = constants.%HasG.type] {} {}
+// CHECK:STDOUT:   %C.decl: type = class_decl @C [template = constants.%C] {} {}
+// CHECK:STDOUT:   %H.decl: %H.type = fn_decl @H [template = constants.%H] {
+// CHECK:STDOUT:     %c.patt: %C = binding_pattern c
+// CHECK:STDOUT:     %c.param_patt: %C = value_param_pattern %c.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %C.ref.loc21: type = name_ref C, file.%C.decl [template = constants.%C]
+// CHECK:STDOUT:     %c.param: %C = value_param runtime_param0
+// CHECK:STDOUT:     %c: %C = bind_name c, %c.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasF {
+// CHECK:STDOUT:   %Self: %HasF.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self.1]
+// CHECK:STDOUT:   %F.decl: %F.type.1 = fn_decl @F.1 [template = constants.%F.1] {} {}
+// CHECK:STDOUT:   %.loc5: %.2 = assoc_entity element0, %F.decl [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .F = %.loc5
+// CHECK:STDOUT:   witness = (%F.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasG {
+// CHECK:STDOUT:   %Self: %HasG.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self.2]
+// CHECK:STDOUT:   %G.decl: %G.type.1 = fn_decl @G.1 [template = constants.%G.1] {} {}
+// CHECK:STDOUT:   %.loc9: %.4 = assoc_entity element0, %G.decl [template = constants.%.5]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .G = %.loc9
+// CHECK:STDOUT:   witness = (%G.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.1: %Self.ref as %HasF.ref {
+// CHECK:STDOUT:   %F.decl: %F.type.2 = fn_decl @F.2 [template = constants.%F.2] {} {}
+// CHECK:STDOUT:   %.loc13: <witness> = interface_witness (%F.decl) [template = constants.%.6]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .F = %F.decl
+// CHECK:STDOUT:   witness = %.loc13
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.2: %Self.ref as %HasG.ref {
+// CHECK:STDOUT:   %G.decl: %G.type.2 = fn_decl @G.2 [template = constants.%G.2] {} {}
+// CHECK:STDOUT:   %.loc16: <witness> = interface_witness (%G.decl) [template = constants.%.7]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .G = %G.decl
+// CHECK:STDOUT:   witness = %.loc16
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @C {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%C [template = constants.%C]
+// CHECK:STDOUT:     %HasF.ref: type = name_ref HasF, file.%HasF.decl [template = constants.%HasF.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%C [template = constants.%C]
+// CHECK:STDOUT:     %HasG.ref: type = name_ref HasG, file.%HasG.decl [template = constants.%HasG.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc19: <witness> = complete_type_witness %.8 [template = constants.%.9]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%C
+// CHECK:STDOUT:   extend name_scope2
+// CHECK:STDOUT:   extend name_scope3
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @F.1(@HasF.%Self: %HasF.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @G.1(@HasG.%Self: %HasG.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @F.2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @G.2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @H(%c.param_patt: %C) {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %C.ref.loc22: type = name_ref C, file.%C.decl [template = constants.%C]
+// CHECK:STDOUT:   %F.ref.loc22: %.2 = name_ref F, @HasF.%.loc5 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc22: %F.type.1 = interface_witness_access constants.%.6, element0 [template = constants.%F.2]
+// CHECK:STDOUT:   %F.call.loc22: init %.1 = call %.loc22()
+// CHECK:STDOUT:   %c.ref.loc23: %C = name_ref c, %c
+// CHECK:STDOUT:   %F.ref.loc23: %.2 = name_ref F, @HasF.%.loc5 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc23: %F.type.1 = interface_witness_access constants.%.6, element0 [template = constants.%F.2]
+// CHECK:STDOUT:   %F.call.loc23: init %.1 = call %.loc23()
+// CHECK:STDOUT:   %C.ref.loc24: type = name_ref C, file.%C.decl [template = constants.%C]
+// CHECK:STDOUT:   %G.ref.loc24: %.4 = name_ref G, @HasG.%.loc9 [template = constants.%.5]
+// CHECK:STDOUT:   %.loc24: %G.type.1 = interface_witness_access constants.%.7, element0 [template = constants.%G.2]
+// CHECK:STDOUT:   %G.call.loc24: init %.1 = call %.loc24()
+// CHECK:STDOUT:   %c.ref.loc25: %C = name_ref c, %c
+// CHECK:STDOUT:   %G.ref.loc25: %.4 = name_ref G, @HasG.%.loc9 [template = constants.%.5]
+// CHECK:STDOUT:   %.loc25: %G.type.1 = interface_witness_access constants.%.7, element0 [template = constants.%G.2]
+// CHECK:STDOUT:   %G.call.loc25: init %.1 = call %.loc25()
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @F.1(constants.%Self.1) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @G.1(constants.%Self.2) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @F.1(constants.%C) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @G.1(constants.%C) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- fail_ambiguous_impls.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %HasA1.type: type = interface_type @HasA1 [template]
+// CHECK:STDOUT:   %Self.1: %HasA1.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %A.type.1: type = fn_type @A.1 [template]
+// CHECK:STDOUT:   %.1: type = tuple_type () [template]
+// CHECK:STDOUT:   %A.1: %A.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.2: type = assoc_entity_type %HasA1.type, %A.type.1 [template]
+// CHECK:STDOUT:   %.3: %.2 = assoc_entity element0, @HasA1.%A.decl [template]
+// CHECK:STDOUT:   %HasA2.type: type = interface_type @HasA2 [template]
+// CHECK:STDOUT:   %Self.2: %HasA2.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %A.type.2: type = fn_type @A.2 [template]
+// CHECK:STDOUT:   %A.2: %A.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.4: type = assoc_entity_type %HasA2.type, %A.type.2 [template]
+// CHECK:STDOUT:   %.5: %.4 = assoc_entity element0, @HasA2.%A.decl [template]
+// CHECK:STDOUT:   %D: type = class_type @D [template]
+// CHECK:STDOUT:   %A.type.3: type = fn_type @A.3 [template]
+// CHECK:STDOUT:   %A.3: %A.type.3 = struct_value () [template]
+// CHECK:STDOUT:   %.6: <witness> = interface_witness (%A.3) [template]
+// CHECK:STDOUT:   %A.type.4: type = fn_type @A.4 [template]
+// CHECK:STDOUT:   %A.4: %A.type.4 = struct_value () [template]
+// CHECK:STDOUT:   %.7: <witness> = interface_witness (%A.4) [template]
+// CHECK:STDOUT:   %.8: type = struct_type {} [template]
+// CHECK:STDOUT:   %.9: <witness> = complete_type_witness %.8 [template]
+// CHECK:STDOUT:   %B.type: type = fn_type @B [template]
+// CHECK:STDOUT:   %B: %B.type = struct_value () [template]
+// CHECK:STDOUT:   %.10: type = ptr_type %.8 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .HasA1 = %HasA1.decl
+// CHECK:STDOUT:     .HasA2 = %HasA2.decl
+// CHECK:STDOUT:     .D = %D.decl
+// CHECK:STDOUT:     .B = %B.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %HasA1.decl: type = interface_decl @HasA1 [template = constants.%HasA1.type] {} {}
+// CHECK:STDOUT:   %HasA2.decl: type = interface_decl @HasA2 [template = constants.%HasA2.type] {} {}
+// CHECK:STDOUT:   %D.decl: type = class_decl @D [template = constants.%D] {} {}
+// CHECK:STDOUT:   %B.decl: %B.type = fn_decl @B [template = constants.%B] {
+// CHECK:STDOUT:     %d.patt: %D = binding_pattern d
+// CHECK:STDOUT:     %d.param_patt: %D = value_param_pattern %d.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %D.ref.loc21: type = name_ref D, file.%D.decl [template = constants.%D]
+// CHECK:STDOUT:     %d.param: %D = value_param runtime_param0
+// CHECK:STDOUT:     %d: %D = bind_name d, %d.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasA1 {
+// CHECK:STDOUT:   %Self: %HasA1.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self.1]
+// CHECK:STDOUT:   %A.decl: %A.type.1 = fn_decl @A.1 [template = constants.%A.1] {} {}
+// CHECK:STDOUT:   %.loc5: %.2 = assoc_entity element0, %A.decl [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .A = %.loc5
+// CHECK:STDOUT:   witness = (%A.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasA2 {
+// CHECK:STDOUT:   %Self: %HasA2.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self.2]
+// CHECK:STDOUT:   %A.decl: %A.type.2 = fn_decl @A.2 [template = constants.%A.2] {} {}
+// CHECK:STDOUT:   %.loc9: %.4 = assoc_entity element0, %A.decl [template = constants.%.5]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .A = %.loc9
+// CHECK:STDOUT:   witness = (%A.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.1: %Self.ref as %HasA1.ref {
+// CHECK:STDOUT:   %A.decl: %A.type.3 = fn_decl @A.3 [template = constants.%A.3] {} {}
+// CHECK:STDOUT:   %.loc13: <witness> = interface_witness (%A.decl) [template = constants.%.6]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .A = %A.decl
+// CHECK:STDOUT:   witness = %.loc13
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.2: %Self.ref as %HasA2.ref {
+// CHECK:STDOUT:   %A.decl: %A.type.4 = fn_decl @A.4 [template = constants.%A.4] {} {}
+// CHECK:STDOUT:   %.loc16: <witness> = interface_witness (%A.decl) [template = constants.%.7]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .A = %A.decl
+// CHECK:STDOUT:   witness = %.loc16
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @D {
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%D [template = constants.%D]
+// CHECK:STDOUT:     %HasA1.ref: type = name_ref HasA1, file.%HasA1.decl [template = constants.%HasA1.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%D [template = constants.%D]
+// CHECK:STDOUT:     %HasA2.ref: type = name_ref HasA2, file.%HasA2.decl [template = constants.%HasA2.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc19: <witness> = complete_type_witness %.8 [template = constants.%.9]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%D
+// CHECK:STDOUT:   extend name_scope2
+// CHECK:STDOUT:   extend name_scope3
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @A.1(@HasA1.%Self: %HasA1.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @A.2(@HasA2.%Self: %HasA2.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @A.3() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @A.4() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @B(%d.param_patt: %D) {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %D.ref.loc26: type = name_ref D, file.%D.decl [template = constants.%D]
+// CHECK:STDOUT:   %A.ref.loc26: <error> = name_ref A, <error> [template = <error>]
+// CHECK:STDOUT:   %d.ref: %D = name_ref d, %d
+// CHECK:STDOUT:   %A.ref.loc31: <error> = name_ref A, <error> [template = <error>]
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @A.1(constants.%Self.1) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @A.2(constants.%Self.2) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @A.1(constants.%D) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @A.2(constants.%D) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- different_impl_and_base.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %HasI.type: type = interface_type @HasI [template]
+// CHECK:STDOUT:   %Self: %HasI.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %I.type.1: type = fn_type @I.1 [template]
+// CHECK:STDOUT:   %.1: type = tuple_type () [template]
+// CHECK:STDOUT:   %I.1: %I.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.2: type = assoc_entity_type %HasI.type, %I.type.1 [template]
+// CHECK:STDOUT:   %.3: %.2 = assoc_entity element0, @HasI.%I.decl [template]
+// CHECK:STDOUT:   %B: type = class_type @B [template]
+// CHECK:STDOUT:   %J.type: type = fn_type @J [template]
+// CHECK:STDOUT:   %J: %J.type = struct_value () [template]
+// CHECK:STDOUT:   %.4: type = struct_type {} [template]
+// CHECK:STDOUT:   %.5: <witness> = complete_type_witness %.4 [template]
+// CHECK:STDOUT:   %E: type = class_type @E [template]
+// CHECK:STDOUT:   %.6: type = ptr_type %.4 [template]
+// CHECK:STDOUT:   %.7: type = unbound_element_type %E, %B [template]
+// CHECK:STDOUT:   %I.type.2: type = fn_type @I.2 [template]
+// CHECK:STDOUT:   %I.2: %I.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.8: <witness> = interface_witness (%I.2) [template]
+// CHECK:STDOUT:   %.9: type = struct_type {.base: %B} [template]
+// CHECK:STDOUT:   %.10: <witness> = complete_type_witness %.9 [template]
+// CHECK:STDOUT:   %H.type: type = fn_type @H [template]
+// CHECK:STDOUT:   %H: %H.type = struct_value () [template]
+// CHECK:STDOUT:   %.11: type = struct_type {.base: %.6} [template]
+// CHECK:STDOUT:   %.12: type = ptr_type %.9 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .HasI = %HasI.decl
+// CHECK:STDOUT:     .B = %B.decl
+// CHECK:STDOUT:     .E = %E.decl
+// CHECK:STDOUT:     .H = %H.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %HasI.decl: type = interface_decl @HasI [template = constants.%HasI.type] {} {}
+// CHECK:STDOUT:   %B.decl: type = class_decl @B [template = constants.%B] {} {}
+// CHECK:STDOUT:   %E.decl: type = class_decl @E [template = constants.%E] {} {}
+// CHECK:STDOUT:   %H.decl: %H.type = fn_decl @H [template = constants.%H] {
+// CHECK:STDOUT:     %e.patt: %E = binding_pattern e
+// CHECK:STDOUT:     %e.param_patt: %E = value_param_pattern %e.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %E.ref.loc19: type = name_ref E, file.%E.decl [template = constants.%E]
+// CHECK:STDOUT:     %e.param: %E = value_param runtime_param0
+// CHECK:STDOUT:     %e: %E = bind_name e, %e.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasI {
+// CHECK:STDOUT:   %Self: %HasI.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
+// CHECK:STDOUT:   %I.decl: %I.type.1 = fn_decl @I.1 [template = constants.%I.1] {} {}
+// CHECK:STDOUT:   %.loc5: %.2 = assoc_entity element0, %I.decl [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .I = %.loc5
+// CHECK:STDOUT:   witness = (%I.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl: %Self.ref as %HasI.ref {
+// CHECK:STDOUT:   %I.decl: %I.type.2 = fn_decl @I.2 [template = constants.%I.2] {} {}
+// CHECK:STDOUT:   %.loc14: <witness> = interface_witness (%I.decl) [template = constants.%.8]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .I = %I.decl
+// CHECK:STDOUT:   witness = %.loc14
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @B {
+// CHECK:STDOUT:   %J.decl: %J.type = fn_decl @J [template = constants.%J] {} {}
+// CHECK:STDOUT:   %.loc10: <witness> = complete_type_witness %.4 [template = constants.%.5]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%B
+// CHECK:STDOUT:   .J = %J.decl
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @E {
+// CHECK:STDOUT:   %B.ref: type = name_ref B, file.%B.decl [template = constants.%B]
+// CHECK:STDOUT:   %.loc13: %.7 = base_decl %B, element0 [template]
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%E [template = constants.%E]
+// CHECK:STDOUT:     %HasI.ref: type = name_ref HasI, file.%HasI.decl [template = constants.%HasI.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc17: <witness> = complete_type_witness %.9 [template = constants.%.10]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%E
+// CHECK:STDOUT:   .base = %.loc13
+// CHECK:STDOUT:   extend name_scope3
+// CHECK:STDOUT:   extend name_scope2
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @I.1(@HasI.%Self: %HasI.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @J() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @I.2() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @H(%e.param_patt: %E) {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %E.ref.loc20: type = name_ref E, file.%E.decl [template = constants.%E]
+// CHECK:STDOUT:   %I.ref.loc20: %.2 = name_ref I, @HasI.%.loc5 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc20: %I.type.1 = interface_witness_access constants.%.8, element0 [template = constants.%I.2]
+// CHECK:STDOUT:   %I.call.loc20: init %.1 = call %.loc20()
+// CHECK:STDOUT:   %e.ref.loc21: %E = name_ref e, %e
+// CHECK:STDOUT:   %I.ref.loc21: %.2 = name_ref I, @HasI.%.loc5 [template = constants.%.3]
+// CHECK:STDOUT:   %.loc21: %I.type.1 = interface_witness_access constants.%.8, element0 [template = constants.%I.2]
+// CHECK:STDOUT:   %I.call.loc21: init %.1 = call %.loc21()
+// CHECK:STDOUT:   %E.ref.loc22: type = name_ref E, file.%E.decl [template = constants.%E]
+// CHECK:STDOUT:   %J.ref.loc22: %J.type = name_ref J, @B.%J.decl [template = constants.%J]
+// CHECK:STDOUT:   %J.call.loc22: init %.1 = call %J.ref.loc22()
+// CHECK:STDOUT:   %e.ref.loc23: %E = name_ref e, %e
+// CHECK:STDOUT:   %J.ref.loc23: %J.type = name_ref J, @B.%J.decl [template = constants.%J]
+// CHECK:STDOUT:   %J.call.loc23: init %.1 = call %J.ref.loc23()
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @I.1(constants.%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @I.1(constants.%E) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- fail_ambiguous_impl_and_base.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %Base: type = class_type @Base [template]
+// CHECK:STDOUT:   %K.type.1: type = fn_type @K.1 [template]
+// CHECK:STDOUT:   %.1: type = tuple_type () [template]
+// CHECK:STDOUT:   %K.1: %K.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.2: type = struct_type {} [template]
+// CHECK:STDOUT:   %.3: <witness> = complete_type_witness %.2 [template]
+// CHECK:STDOUT:   %HasK.type: type = interface_type @HasK [template]
+// CHECK:STDOUT:   %Self: %HasK.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %K.type.2: type = fn_type @K.2 [template]
+// CHECK:STDOUT:   %K.2: %K.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.4: type = assoc_entity_type %HasK.type, %K.type.2 [template]
+// CHECK:STDOUT:   %.5: %.4 = assoc_entity element0, @HasK.%K.decl [template]
+// CHECK:STDOUT:   %L: type = class_type @L [template]
+// CHECK:STDOUT:   %.6: type = ptr_type %.2 [template]
+// CHECK:STDOUT:   %.7: type = unbound_element_type %L, %Base [template]
+// CHECK:STDOUT:   %K.type.3: type = fn_type @K.3 [template]
+// CHECK:STDOUT:   %K.3: %K.type.3 = struct_value () [template]
+// CHECK:STDOUT:   %.8: <witness> = interface_witness (%K.3) [template]
+// CHECK:STDOUT:   %.9: type = struct_type {.base: %Base} [template]
+// CHECK:STDOUT:   %.10: <witness> = complete_type_witness %.9 [template]
+// CHECK:STDOUT:   %M.type: type = fn_type @M [template]
+// CHECK:STDOUT:   %M: %M.type = struct_value () [template]
+// CHECK:STDOUT:   %.11: type = struct_type {.base: %.6} [template]
+// CHECK:STDOUT:   %.12: type = ptr_type %.9 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .Base = %Base.decl
+// CHECK:STDOUT:     .HasK = %HasK.decl
+// CHECK:STDOUT:     .L = %L.decl
+// CHECK:STDOUT:     .M = %M.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %Base.decl: type = class_decl @Base [template = constants.%Base] {} {}
+// CHECK:STDOUT:   %HasK.decl: type = interface_decl @HasK [template = constants.%HasK.type] {} {}
+// CHECK:STDOUT:   %L.decl: type = class_decl @L [template = constants.%L] {} {}
+// CHECK:STDOUT:   %M.decl: %M.type = fn_decl @M [template = constants.%M] {
+// CHECK:STDOUT:     %l.patt: %L = binding_pattern l
+// CHECK:STDOUT:     %l.param_patt: %L = value_param_pattern %l.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %L.ref.loc19: type = name_ref L, file.%L.decl [template = constants.%L]
+// CHECK:STDOUT:     %l.param: %L = value_param runtime_param0
+// CHECK:STDOUT:     %l: %L = bind_name l, %l.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasK {
+// CHECK:STDOUT:   %Self: %HasK.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self]
+// CHECK:STDOUT:   %K.decl: %K.type.2 = fn_decl @K.2 [template = constants.%K.2] {} {}
+// CHECK:STDOUT:   %.loc9: %.4 = assoc_entity element0, %K.decl [template = constants.%.5]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .K = %.loc9
+// CHECK:STDOUT:   witness = (%K.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl: %Self.ref as %HasK.ref {
+// CHECK:STDOUT:   %K.decl: %K.type.3 = fn_decl @K.3 [template = constants.%K.3] {} {}
+// CHECK:STDOUT:   %.loc14: <witness> = interface_witness (%K.decl) [template = constants.%.8]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .K = %K.decl
+// CHECK:STDOUT:   witness = %.loc14
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @Base {
+// CHECK:STDOUT:   %K.decl: %K.type.1 = fn_decl @K.1 [template = constants.%K.1] {} {}
+// CHECK:STDOUT:   %.loc6: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%Base
+// CHECK:STDOUT:   .K = %K.decl
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @L {
+// CHECK:STDOUT:   %Base.ref: type = name_ref Base, file.%Base.decl [template = constants.%Base]
+// CHECK:STDOUT:   %.loc13: %.7 = base_decl %Base, element0 [template]
+// CHECK:STDOUT:   impl_decl @impl [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%L [template = constants.%L]
+// CHECK:STDOUT:     %HasK.ref: type = name_ref HasK, file.%HasK.decl [template = constants.%HasK.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %.loc17: <witness> = complete_type_witness %.9 [template = constants.%.10]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%L
+// CHECK:STDOUT:   .base = %.loc13
+// CHECK:STDOUT:   extend name_scope2
+// CHECK:STDOUT:   extend name_scope3
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @K.1() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @K.2(@HasK.%Self: %HasK.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @K.3() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @M(%l.param_patt: %L) {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %L.ref.loc24: type = name_ref L, file.%L.decl [template = constants.%L]
+// CHECK:STDOUT:   %K.ref.loc24: <error> = name_ref K, <error> [template = <error>]
+// CHECK:STDOUT:   %l.ref: %L = name_ref l, %l
+// CHECK:STDOUT:   %K.ref.loc28: <error> = name_ref K, <error> [template = <error>]
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @K.2(constants.%Self) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @K.2(constants.%L) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: --- ambiguity_hidden.carbon
+// CHECK:STDOUT:
+// CHECK:STDOUT: constants {
+// CHECK:STDOUT:   %NBase: type = class_type @NBase [template]
+// CHECK:STDOUT:   %N.type.1: type = fn_type @N.1 [template]
+// CHECK:STDOUT:   %.1: type = tuple_type () [template]
+// CHECK:STDOUT:   %N.1: %N.type.1 = struct_value () [template]
+// CHECK:STDOUT:   %.2: type = struct_type {} [template]
+// CHECK:STDOUT:   %.3: <witness> = complete_type_witness %.2 [template]
+// CHECK:STDOUT:   %HasN1.type: type = interface_type @HasN1 [template]
+// CHECK:STDOUT:   %Self.1: %HasN1.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %N.type.2: type = fn_type @N.2 [template]
+// CHECK:STDOUT:   %N.2: %N.type.2 = struct_value () [template]
+// CHECK:STDOUT:   %.4: type = assoc_entity_type %HasN1.type, %N.type.2 [template]
+// CHECK:STDOUT:   %.5: %.4 = assoc_entity element0, @HasN1.%N.decl [template]
+// CHECK:STDOUT:   %HasN2.type: type = interface_type @HasN2 [template]
+// CHECK:STDOUT:   %Self.2: %HasN2.type = bind_symbolic_name Self, 0 [symbolic]
+// CHECK:STDOUT:   %N.type.3: type = fn_type @N.3 [template]
+// CHECK:STDOUT:   %N.3: %N.type.3 = struct_value () [template]
+// CHECK:STDOUT:   %.6: type = assoc_entity_type %HasN2.type, %N.type.3 [template]
+// CHECK:STDOUT:   %.7: %.6 = assoc_entity element0, @HasN2.%N.decl [template]
+// CHECK:STDOUT:   %O: type = class_type @O [template]
+// CHECK:STDOUT:   %.8: type = ptr_type %.2 [template]
+// CHECK:STDOUT:   %.9: type = unbound_element_type %O, %NBase [template]
+// CHECK:STDOUT:   %N.type.4: type = fn_type @N.4 [template]
+// CHECK:STDOUT:   %N.4: %N.type.4 = struct_value () [template]
+// CHECK:STDOUT:   %.10: <witness> = interface_witness (%N.4) [template]
+// CHECK:STDOUT:   %N.type.5: type = fn_type @N.5 [template]
+// CHECK:STDOUT:   %N.5: %N.type.5 = struct_value () [template]
+// CHECK:STDOUT:   %.11: <witness> = interface_witness (%N.5) [template]
+// CHECK:STDOUT:   %N.type.6: type = fn_type @N.6 [template]
+// CHECK:STDOUT:   %N.6: %N.type.6 = struct_value () [template]
+// CHECK:STDOUT:   %.12: type = struct_type {.base: %NBase} [template]
+// CHECK:STDOUT:   %.13: <witness> = complete_type_witness %.12 [template]
+// CHECK:STDOUT:   %P.type: type = fn_type @P [template]
+// CHECK:STDOUT:   %P: %P.type = struct_value () [template]
+// CHECK:STDOUT:   %.14: type = struct_type {.base: %.8} [template]
+// CHECK:STDOUT:   %.15: type = ptr_type %.12 [template]
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: imports {
+// CHECK:STDOUT:   %Core: <namespace> = namespace file.%Core.import, [template] {
+// CHECK:STDOUT:     import Core//prelude
+// CHECK:STDOUT:     import Core//prelude/...
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: file {
+// CHECK:STDOUT:   package: <namespace> = namespace [template] {
+// CHECK:STDOUT:     .Core = imports.%Core
+// CHECK:STDOUT:     .NBase = %NBase.decl
+// CHECK:STDOUT:     .HasN1 = %HasN1.decl
+// CHECK:STDOUT:     .HasN2 = %HasN2.decl
+// CHECK:STDOUT:     .O = %O.decl
+// CHECK:STDOUT:     .P = %P.decl
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %Core.import = import Core
+// CHECK:STDOUT:   %NBase.decl: type = class_decl @NBase [template = constants.%NBase] {} {}
+// CHECK:STDOUT:   %HasN1.decl: type = interface_decl @HasN1 [template = constants.%HasN1.type] {} {}
+// CHECK:STDOUT:   %HasN2.decl: type = interface_decl @HasN2 [template = constants.%HasN2.type] {} {}
+// CHECK:STDOUT:   %O.decl: type = class_decl @O [template = constants.%O] {} {}
+// CHECK:STDOUT:   %P.decl: %P.type = fn_decl @P [template = constants.%P] {
+// CHECK:STDOUT:     %o.patt: %O = binding_pattern o
+// CHECK:STDOUT:     %o.param_patt: %O = value_param_pattern %o.patt, runtime_param0
+// CHECK:STDOUT:   } {
+// CHECK:STDOUT:     %O.ref.loc27: type = name_ref O, file.%O.decl [template = constants.%O]
+// CHECK:STDOUT:     %o.param: %O = value_param runtime_param0
+// CHECK:STDOUT:     %o: %O = bind_name o, %o.param
+// CHECK:STDOUT:   }
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasN1 {
+// CHECK:STDOUT:   %Self: %HasN1.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self.1]
+// CHECK:STDOUT:   %N.decl: %N.type.2 = fn_decl @N.2 [template = constants.%N.2] {} {}
+// CHECK:STDOUT:   %.loc9: %.4 = assoc_entity element0, %N.decl [template = constants.%.5]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .N = %.loc9
+// CHECK:STDOUT:   witness = (%N.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: interface @HasN2 {
+// CHECK:STDOUT:   %Self: %HasN2.type = bind_symbolic_name Self, 0 [symbolic = constants.%Self.2]
+// CHECK:STDOUT:   %N.decl: %N.type.3 = fn_decl @N.3 [template = constants.%N.3] {} {}
+// CHECK:STDOUT:   %.loc13: %.6 = assoc_entity element0, %N.decl [template = constants.%.7]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = %Self
+// CHECK:STDOUT:   .N = %.loc13
+// CHECK:STDOUT:   witness = (%N.decl)
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.1: %Self.ref as %HasN1.ref {
+// CHECK:STDOUT:   %N.decl: %N.type.4 = fn_decl @N.4 [template = constants.%N.4] {} {}
+// CHECK:STDOUT:   %.loc18: <witness> = interface_witness (%N.decl) [template = constants.%.10]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .N = %N.decl
+// CHECK:STDOUT:   witness = %.loc18
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: impl @impl.2: %Self.ref as %HasN2.ref {
+// CHECK:STDOUT:   %N.decl: %N.type.5 = fn_decl @N.5 [template = constants.%N.5] {} {}
+// CHECK:STDOUT:   %.loc21: <witness> = interface_witness (%N.decl) [template = constants.%.11]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .N = %N.decl
+// CHECK:STDOUT:   witness = %.loc21
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @NBase {
+// CHECK:STDOUT:   %N.decl: %N.type.1 = fn_decl @N.1 [template = constants.%N.1] {} {}
+// CHECK:STDOUT:   %.loc6: <witness> = complete_type_witness %.2 [template = constants.%.3]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%NBase
+// CHECK:STDOUT:   .N = %N.decl
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: class @O {
+// CHECK:STDOUT:   %NBase.ref: type = name_ref NBase, file.%NBase.decl [template = constants.%NBase]
+// CHECK:STDOUT:   %.loc17: %.9 = base_decl %NBase, element0 [template]
+// CHECK:STDOUT:   impl_decl @impl.1 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%O [template = constants.%O]
+// CHECK:STDOUT:     %HasN1.ref: type = name_ref HasN1, file.%HasN1.decl [template = constants.%HasN1.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   impl_decl @impl.2 [template] {} {
+// CHECK:STDOUT:     %Self.ref: type = name_ref Self, constants.%O [template = constants.%O]
+// CHECK:STDOUT:     %HasN2.ref: type = name_ref HasN2, file.%HasN2.decl [template = constants.%HasN2.type]
+// CHECK:STDOUT:   }
+// CHECK:STDOUT:   %N.decl: %N.type.6 = fn_decl @N.6 [template = constants.%N.6] {} {}
+// CHECK:STDOUT:   %.loc25: <witness> = complete_type_witness %.12 [template = constants.%.13]
+// CHECK:STDOUT:
+// CHECK:STDOUT: !members:
+// CHECK:STDOUT:   .Self = constants.%O
+// CHECK:STDOUT:   .base = %.loc17
+// CHECK:STDOUT:   .N = %N.decl
+// CHECK:STDOUT:   extend name_scope2
+// CHECK:STDOUT:   extend name_scope3
+// CHECK:STDOUT:   extend name_scope4
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @N.1() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @N.2(@HasN1.%Self: %HasN1.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: generic fn @N.3(@HasN2.%Self: %HasN2.type) {
+// CHECK:STDOUT:
+// CHECK:STDOUT:   fn();
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @N.4() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @N.5() {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @N.6();
+// CHECK:STDOUT:
+// CHECK:STDOUT: fn @P(%o.param_patt: %O) {
+// CHECK:STDOUT: !entry:
+// CHECK:STDOUT:   %O.ref.loc28: type = name_ref O, file.%O.decl [template = constants.%O]
+// CHECK:STDOUT:   %N.ref.loc28: %N.type.6 = name_ref N, @O.%N.decl [template = constants.%N.6]
+// CHECK:STDOUT:   %N.call.loc28: init %.1 = call %N.ref.loc28()
+// CHECK:STDOUT:   %o.ref: %O = name_ref o, %o
+// CHECK:STDOUT:   %N.ref.loc29: %N.type.6 = name_ref N, @O.%N.decl [template = constants.%N.6]
+// CHECK:STDOUT:   %N.call.loc29: init %.1 = call %N.ref.loc29()
+// CHECK:STDOUT:   return
+// CHECK:STDOUT: }
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @N.2(constants.%Self.1) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @N.3(constants.%Self.2) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @N.2(constants.%O) {}
+// CHECK:STDOUT:
+// CHECK:STDOUT: specific @N.3(constants.%O) {}
+// CHECK:STDOUT:
diff --git a/toolchain/diagnostics/coverage_test.cpp b/toolchain/diagnostics/coverage_test.cpp
index 9f857641a552..f21d8936d664 100644
--- a/toolchain/diagnostics/coverage_test.cpp
+++ b/toolchain/diagnostics/coverage_test.cpp
@@ -50,7 +50,6 @@ constexpr DiagnosticKind UntestedDiagnosticKinds[] = {
     DiagnosticKind::MismatchedIndentInString,
     DiagnosticKind::ModifierPrivateNotAllowed,
     DiagnosticKind::MultiLineStringWithDoubleQuotes,
-    DiagnosticKind::NameAmbiguousDueToExtend,
     DiagnosticKind::TooManyDigits,
     DiagnosticKind::UnaryOperatorRequiresWhitespace,
     DiagnosticKind::UnicodeEscapeSurrogate,
diff --git a/toolchain/sem_ir/name_scope.h b/toolchain/sem_ir/name_scope.h
index 4588e62572e0..d3d1a740e1a8 100644
--- a/toolchain/sem_ir/name_scope.h
+++ b/toolchain/sem_ir/name_scope.h
@@ -87,8 +87,7 @@ struct NameScope : Printable<NameScope> {
   // needs to describe the `T*` argument.
   //
   // Small vector size is set to 1: we expect that there will rarely be more
-  // than a single extended scope. Currently the only kind of extended scope is
-  // a base class, and there can be only one of those per scope.
+  // than a single extended scope.
   // TODO: Revisit this once we have more kinds of extended scope and data.
   // TODO: Consider using something like `TinyPtrVector` for this.
   llvm::SmallVector<NameScopeId, 1> extended_scopes;