anchor.diff:  
     if (!isLegacy) testDir = toNnbdPath(testDir);
   
  -  var testArgs = [
  -    "--mode=release",
  -    if (!isLegacy) ...[
  -      "--enable-experiment=non-nullable",
  -      "--nnbd=strong",
  -    ],
  -    "--compiler=${compilers.join(',')}",
  -    testDir,
  -  ];
  +  // DDC doesn't have a Mac bot so when running DDC tests on a Mac, use a manual
  +  // configuration. Otherwise, use the right named configuration.
  +  List<String> testArgs;
  +  if (Platform.isLinux || compiler != "ddc") {
  +    var configuration = configurations[compiler];
  +    if (!Platform.isLinux) {
  +      // TODO(rnystrom): We'll probably never need to run this script on
  +      // Windows, but if we do... do that.
  +      configuration = configuration.replaceAll("linux", "mac");
  +    }
  +
  +    testArgs = ["-n$configuration", testDir];
  +  } else {
  +    testArgs = [
  +      "--mode=release",
  +      if (!isLegacy) ...[
  +        "--enable-experiment=non-nullable",
  +        "--nnbd=strong",
  +      ],
  +      "--compiler=${compilerNames[compiler]}",
  +      testDir,
  +    ];
  +  }
   
     print("Running tools/test.py ${testArgs.join(' ')}");
     await runProcessAsync("tools/test.py", testArgs);
  
positive.code:       negatable: false,
        callback: (flag) => isLegacy = flag);
  
    argParser.addMultiOption("compiler",
        abbr: "c",
        help: "Which Dart implementations to run the tests on.",
        allowed: ["analyzer", "cfe", "dart2js", "ddc", "vm"],
        callback: (implementations) {
      compilers.addAll(implementations.map((name) => compilerNames[name]));
    });
  
    if (arguments.contains("--help")) {
      showUsage(argParser);
  
negative.code:   "vm": "dartk",
  };
  
  const configurations = {
    "analyzer": "analyzer-asserts-strong-linux",
    "cfe": "cfe-strong-linux",
    "dart2js": "dart2js-weak-linux-x64-d8",
    "ddc": "dartdevk-strong-linux-release-chrome",
    "vm": "dartk-strong-linux-release-x64",
  };
  
  void main(List<String> arguments) async {
    var testDir = "";
    var isLegacy = false;
    var compiler = "ddc";
  
    var argParser = ArgParser();
    argParser.addFlag("legacy",
  