anchor.diff:      // The main test library doesn't depend on b.dart, because no change to
       // b.dart can possibly affect the serialized element model for it.
       checkLacksDependency(absUri('/b.dart'), 'b.dart');
  +  }
  +
  +  test_dependencies_import_unused() {
  +    addNamedSource('/a.dart', '');
  +    serializeLibraryText('import "a.dart";', allowErrors: true);
  +    // The main test library depends on a.dart, even though it doesn't use any
  +    // names defined in a.dart, because a change to a.dart might cause it to
  +    // start exporting a name that the main test library *does* use.
  +    checkHasDependency(absUri('/a.dart'), 'a.dart');
     }
   
     test_dependencies_parts() {
  
positive.code:     checkHasDependency(absUri('/c.dart'), 'c.dart');
    }
  
    test_dependencies_import_transitive_closure() {
      addNamedSource(
          '/a.dart', 'library a; import "b.dart"; class A extends B {}');
  
negative.code:     checkTypeRef(typeRef, null, null, checkAstDerivedData ? expectedName : null,
          expectedPrefix: expectedPrefix,
          expectedKind: PrelinkedReferenceKind.unresolved);
    }
  
    fail_dependencies_export_to_export_unused() {
      // TODO(paulberry): fix this test.
      addNamedSource('/a.dart', 'export "b.dart";');
      addNamedSource('/b.dart', '');
      serializeLibraryText('export "a.dart";');
      // The main test library depends on b.dart, even though it doesn't
      // re-export any names defined in b.dart, because a change to b.dart might
      // cause it to start exporting a name that the main test library *does*
      // use.
      checkHasDependency(absUri('/b.dart'), 'b.dart');
    }
  
    fail_dependencies_export_unused() {
      // TODO(paulberry): fix this test.
      addNamedSource('/a.dart', '');
      serializeLibraryText('export "a.dart";');
      // The main test library depends on a.dart, even though it doesn't
      // re-export any names defined in a.dart, because a change to a.dart might
      // cause it to start exporting a name that the main test library *will*
      // re-export.
      checkHasDependency(absUri('/a.dart'), 'a.dart');
    }
  
    fail_enum_value_documented() {
  