anchor.diff:  
         test("404s for a nonexistent file", () async {
           var handler = packagesHandler(resolver: resolver);
  -        var request = new Request(
  -            "GET", Uri.parse("http://example.com/foo/bar.dart"));
  +        var request =
  +            new Request("GET", Uri.parse("http://example.com/foo/bar.dart"));
           var response = await handler(request);
           expect(response.statusCode, equals(404));
         });
  
positive.code:       var handler = packagesDirHandler();
        var request = new Request(
            "GET",
            Uri.parse(
                "http://example.com/packages/shelf_packages_handler/"
                "shelf_packages_handler.dart"));
        var response = await handler(request);
        expect(response.statusCode, equals(200));
        expect(await response.readAsString(),
            contains("Handler packagesHandler"));
      });
  
      test("supports a directory deep in the URL", () async {
        var handler = packagesDirHandler();
        var request = new Request(
            "GET",
            Uri.parse(
                "http://example.com/foo/bar/very/deep/packages/"
                "shelf_packages_handler/shelf_packages_handler.dart"));
        var response = await handler(request);
        expect(response.statusCode, equals(200));
        expect(await response.readAsString(),
            contains("Handler packagesHandler"));
      });
  
      test("404s for a URL without a packages directory", () async {
        var handler = packagesDirHandler();
        var request = new Request(
            "GET",
            Uri.parse(
                "http://example.com/shelf_packages_handler/"
                "shelf_packages_handler.dart"));
        var response = await handler(request);
        expect(response.statusCode, equals(404));
  
negative.code: void main() {
    var dir;
    setUp(() {
      dir =
          Directory.systemTemp.createTempSync("shelf_packages_handler_test").path;
      new Directory(dir).createSync();
      new Directory("$dir/foo").createSync();
      new File("$dir/foo/foo.dart")
  