anchor.diff:  import "package:front_end/src/api_prototype/memory_file_system.dart"
       show MemoryFileSystem;
   
  +import 'package:front_end/src/fasta/fasta_codes.dart' show LocatedMessage;
  +
  +import 'package:front_end/src/fasta/severity.dart' show Severity;
  +
   Directory outDir;
   
   main() async {
  
positive.code:   var options = new CompilerOptions()
      ..sdkRoot = sdkRoot
      ..librariesSpecificationUri = Uri.base.resolve("sdk/lib/libraries.json")
      ..strongMode = false;
    return options;
  }
  
negative.code:   await runPassingTest(testDisappearingLibrary);
    await runPassingTest(testDeferredLibrary);
    await runPassingTest(testStrongModeMixins);
    await runFailingTest(
        testStrongModeMixins2,
        "testStrongModeMixins2_a.dart: Error: "
        "The parameter 'value' of the method 'A::child' has type");
  }
  
  void runFailingTest(dynamic test, String expectContains) async {
  