diff --git a/lib/src/backend/declarer.dart b/lib/src/backend/declarer.dart
index 1d40c5524..4e8851d4f 100644
--- a/lib/src/backend/declarer.dart
+++ b/lib/src/backend/declarer.dart
@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:collection/collection.dart';
 import 'package:stack_trace/stack_trace.dart';
 
 import '../frontend/timeout.dart';
@@ -13,7 +14,6 @@ import 'group_entry.dart';
 import 'invoker.dart';
 import 'metadata.dart';
 import 'test.dart';
-import 'test_platform.dart';
 
 /// A class that manages the state of tests as they're declared.
 ///
@@ -23,9 +23,6 @@ import 'test_platform.dart';
 /// for a block using [Declarer.declare], and it can be accessed using
 /// [Declarer.current].
 class Declarer {
-  /// All test plaforms that are defined for the current test run.
-  final List<TestPlatform> _allPlatforms;
-
   /// The parent declarer, or `null` if this corresponds to the root group.
   final Declarer _parent;
 
@@ -39,6 +36,10 @@ class Declarer {
   /// and of the test suite.
   final Metadata _metadata;
 
+  /// The set of variables that are valid for platform selectors, in addition to
+  /// the built-in variables that are allowed everywhere.
+  final Set<String> _platformVariables;
+
   /// The stack trace for this group.
   final Trace _trace;
 
@@ -88,17 +89,30 @@ class Declarer {
   /// If [metadata] is passed, it's used as the metadata for the implicit root
   /// group.
   ///
+  /// The [platformVariables] are the set of variables that are valid for
+  /// platform selectors in test and group metadata, in addition to the built-in
+  /// variables that are allowed everywhere.
+  ///
   /// If [collectTraces] is `true`, this will set [GroupEntry.trace] for all
   /// entries built by the declarer. Note that this can be noticeably slow when
   /// thousands of tests are being declared (see #457).
   ///
   /// If [noRetry] is `true` tests will be run at most once.
-  Declarer(List<TestPlatform> allPlatforms,
-      {Metadata metadata, bool collectTraces: false, bool noRetry: false})
-      : this._(allPlatforms, null, null, metadata ?? new Metadata(),
-            collectTraces, null, noRetry);
-
-  Declarer._(this._allPlatforms, this._parent, this._name, this._metadata,
+  Declarer(
+      {Metadata metadata,
+      Set<String> platformVariables,
+      bool collectTraces: false,
+      bool noRetry: false})
+      : this._(
+            null,
+            null,
+            metadata ?? new Metadata(),
+            platformVariables ?? const UnmodifiableSetView.empty(),
+            collectTraces,
+            null,
+            noRetry);
+
+  Declarer._(this._parent, this._name, this._metadata, this._platformVariables,
       this._collectTraces, this._trace, this._noRetry);
 
   /// Runs [body] with this declarer as [Declarer.current].
@@ -123,7 +137,7 @@ class Declarer {
         onPlatform: onPlatform,
         tags: tags,
         retry: _noRetry ? 0 : retry);
-    newMetadata.validatePlatformSelectors(_allPlatforms);
+    newMetadata.validatePlatformSelectors(_platformVariables);
     var metadata = _metadata.merge(newMetadata);
 
     _entries.add(new LocalTest(_prefix(name), metadata, () async {
@@ -165,12 +179,12 @@ class Declarer {
         onPlatform: onPlatform,
         tags: tags,
         retry: _noRetry ? 0 : retry);
-    newMetadata.validatePlatformSelectors(_allPlatforms);
+    newMetadata.validatePlatformSelectors(_platformVariables);
     var metadata = _metadata.merge(newMetadata);
     var trace = _collectTraces ? new Trace.current(2) : null;
 
-    var declarer = new Declarer._(_allPlatforms, this, _prefix(name), metadata,
-        _collectTraces, trace, _noRetry);
+    var declarer = new Declarer._(this, _prefix(name), metadata,
+        _platformVariables, _collectTraces, trace, _noRetry);
     declarer.declare(() {
       // Cast to dynamic to avoid the analyzer complaining about us using the
       // result of a void method.
diff --git a/lib/src/backend/metadata.dart b/lib/src/backend/metadata.dart
index d8441cfca..7ff1a8624 100644
--- a/lib/src/backend/metadata.dart
+++ b/lib/src/backend/metadata.dart
@@ -286,13 +286,14 @@ class Metadata {
         "Dart identifiers.");
   }
 
-  /// Throws a [FormatException] if any [PlatformSelector]s use variables that
-  /// are undefined in [allPlatforms] or other sources of valid variables.
-  void validatePlatformSelectors(List<TestPlatform> allPlatforms) {
-    testOn.validate(allPlatforms);
+  /// Throws a [FormatException] if any [PlatformSelector]s use any variables
+  /// that don't appear either in [validVariables] or in the set of variables
+  /// that are known to be valid for all selectors.
+  void validatePlatformSelectors(Set<String> validVariables) {
+    testOn.validate(validVariables);
     onPlatform.forEach((selector, metadata) {
-      selector.validate(allPlatforms);
-      metadata.validatePlatformSelectors(allPlatforms);
+      selector.validate(validVariables);
+      metadata.validatePlatformSelectors(validVariables);
     });
   }
 
diff --git a/lib/src/backend/platform_selector.dart b/lib/src/backend/platform_selector.dart
index ff964ad5a..be644d39a 100644
--- a/lib/src/backend/platform_selector.dart
+++ b/lib/src/backend/platform_selector.dart
@@ -8,9 +8,10 @@ import 'package:source_span/source_span.dart';
 import 'operating_system.dart';
 import 'test_platform.dart';
 
-/// The set of statically-known valid variable names.
-final _validVariables =
+/// The set of variable names that are valid for all platform selectors.
+final _universalValidVariables =
     new Set<String>.from(["posix", "dart-vm", "browser", "js", "blink"])
+      ..addAll(TestPlatform.builtIn.map((platform) => platform.identifier))
       ..addAll(OperatingSystem.all.map((os) => os.identifier));
 
 /// An expression for selecting certain platforms, including operating systems
@@ -54,17 +55,17 @@ class PlatformSelector {
     }
   }
 
-  /// Throws a [FormatException] if any variables are undefined in
-  /// [allPlatforms] or other sources of valid variables.
-  void validate(Iterable<TestPlatform> allPlatforms) {
+  /// Throws a [FormatException] if this selector uses any variables that don't
+  /// appear either in [validVariables] or in the set of variables that are
+  /// known to be valid for all selectors.
+  void validate(Set<String> validVariables) {
     if (identical(this, all)) return;
 
-    _wrapFormatException(() {
-      _inner.validate((name) {
-        if (_validVariables.contains(name)) return true;
-        return allPlatforms.any((platform) => name == platform.identifier);
-      });
-    }, _span);
+    _wrapFormatException(
+        () => _inner.validate((name) =>
+            _universalValidVariables.contains(name) ||
+            validVariables.contains(name)),
+        _span);
   }
 
   /// Returns whether the selector matches the given [platform] and [os].
diff --git a/lib/src/runner/configuration/suite.dart b/lib/src/runner/configuration/suite.dart
index ac360bd10..6ed34586c 100644
--- a/lib/src/runner/configuration/suite.dart
+++ b/lib/src/runner/configuration/suite.dart
@@ -293,7 +293,9 @@ class SuiteConfiguration {
 
   /// Throws a [FormatException] if [this] refers to any undefined platforms.
   void validatePlatforms(List<TestPlatform> allPlatforms) {
-    _metadata.validatePlatformSelectors(allPlatforms);
+    var validVariables =
+        allPlatforms.map((platform) => platform.identifier).toSet();
+    _metadata.validatePlatformSelectors(validVariables);
 
     if (_platforms != null) {
       for (var selection in _platforms) {
@@ -310,7 +312,7 @@ class SuiteConfiguration {
     }
 
     onPlatform.forEach((selector, config) {
-      selector.validate(allPlatforms);
+      selector.validate(validVariables);
       config.validatePlatforms(allPlatforms);
     });
   }
diff --git a/lib/src/runner/loader.dart b/lib/src/runner/loader.dart
index f74308421..84b3149d0 100644
--- a/lib/src/runner/loader.dart
+++ b/lib/src/runner/loader.dart
@@ -51,19 +51,10 @@ class Loader {
   List<TestPlatform> get allPlatforms =>
       new List.unmodifiable(_platformCallbacks.keys);
 
-  List<Map<String, Object>> get _allPlatformsSerialized {
-    if (__allPlatformsSerialized != null &&
-        __allPlatformsSerialized.length == _platformCallbacks.length) {
-      return __allPlatformsSerialized;
-    }
-
-    __allPlatformsSerialized = _platformCallbacks.keys
-        .map((platform) => platform.serialize())
-        .toList();
-    return __allPlatformsSerialized;
-  }
-
-  List<Map<String, Object>> __allPlatformsSerialized;
+  /// The platform variables supported by this loader, in addition the default
+  /// variables that are always supported.
+  Iterable<String> get _platformVariables =>
+      _platformCallbacks.keys.map((platform) => platform.identifier);
 
   /// Creates a new loader that loads tests on platforms defined in
   /// [Configuration.current].
@@ -146,7 +137,7 @@ class Loader {
       String path, SuiteConfiguration suiteConfig) async* {
     try {
       suiteConfig = suiteConfig.merge(new SuiteConfiguration.fromMetadata(
-          parseMetadata(path, allPlatforms)));
+          parseMetadata(path, _platformVariables.toSet())));
     } on AnalyzerErrorGroup catch (_) {
       // Ignore the analyzer's error, since its formatting is much worse than
       // the VM's or dart2js's.
@@ -195,7 +186,7 @@ class Loader {
         try {
           var plugin = await memo.runOnce(_platformCallbacks[platform]);
           var suite = await plugin.load(path, platform, platformConfig,
-              {"testPlatforms": _allPlatformsSerialized});
+              {"platformVariables": _platformVariables.toList()});
           if (suite != null) _suites.add(suite);
           return suite;
         } catch (error, stackTrace) {
diff --git a/lib/src/runner/parse_metadata.dart b/lib/src/runner/parse_metadata.dart
index 299e861a7..e8aa1ae22 100644
--- a/lib/src/runner/parse_metadata.dart
+++ b/lib/src/runner/parse_metadata.dart
@@ -12,28 +12,29 @@ import 'package:source_span/source_span.dart';
 
 import '../backend/metadata.dart';
 import '../backend/platform_selector.dart';
-import '../backend/test_platform.dart';
 import '../frontend/timeout.dart';
 import '../util/dart.dart';
 import '../utils.dart';
 
 /// Parse the test metadata for the test file at [path].
 ///
-/// The [allTestPlatforms] argument should list all test plaforms that are
-/// defined for the current test run.
+/// The [platformVariables] are the set of variables that are valid for platform
+/// selectors in suite metadata, in addition to the built-in variables that are
+/// allowed everywhere.
 ///
 /// Throws an [AnalysisError] if parsing fails or a [FormatException] if the
 /// test annotations are incorrect.
-Metadata parseMetadata(String path, List<TestPlatform> allTestPlatforms) =>
-    new _Parser(path, allTestPlatforms).parse();
+Metadata parseMetadata(String path, Set<String> platformVariables) =>
+    new _Parser(path, platformVariables).parse();
 
 /// A parser for test suite metadata.
 class _Parser {
   /// The path to the test suite.
   final String _path;
 
-  /// All test plaforms that are defined for the current test run.
-  final List<TestPlatform> _allTestPlatforms;
+  /// The set of variables that are valid for platform selectors, in addition to
+  /// the built-in variables that are allowed everywhere.
+  final Set<String> _platformVariables;
 
   /// All annotations at the top of the file.
   List<Annotation> _annotations;
@@ -41,7 +42,7 @@ class _Parser {
   /// All prefixes defined by imports in this file.
   Set<String> _prefixes;
 
-  _Parser(String path, this._allTestPlatforms) : _path = path {
+  _Parser(String path, this._platformVariables) : _path = path {
     var contents = new File(path).readAsStringSync();
     var directives = parseDirectives(contents, name: path).directives;
     _annotations = directives.isEmpty ? [] : directives.first.metadata;
@@ -123,7 +124,7 @@ class _Parser {
     return _contextualize(
         literal,
         () => new PlatformSelector.parse(literal.stringValue)
-          ..validate(_allTestPlatforms));
+          ..validate(_platformVariables));
   }
 
   /// Parses a `@Retry` annotation.
diff --git a/lib/src/runner/plugin/platform_helpers.dart b/lib/src/runner/plugin/platform_helpers.dart
index c1d2d74de..b41e5ba84 100644
--- a/lib/src/runner/plugin/platform_helpers.dart
+++ b/lib/src/runner/plugin/platform_helpers.dart
@@ -51,7 +51,7 @@ Future<RunnerSuiteController> deserializeSuite(
   var suiteChannel = new MultiChannel(channel.transform(disconnector));
 
   suiteChannel.sink.add({
-    'platform': platform.identifier,
+    'platform': platform.serialize(),
     'metadata': suiteConfig.metadata.serialize(),
     'os': platform == TestPlatform.vm ? currentOS.identifier : null,
     'asciiGlyphs': Platform.isWindows,
@@ -75,7 +75,7 @@ Future<RunnerSuiteController> deserializeSuite(
       // notify the user of the error.
       loadSuiteZone.handleUncaughtError(error, stackTrace);
     } else {
-      completer.completeError(error);
+      completer.completeError(error, stackTrace);
     }
   }
 
diff --git a/lib/src/runner/remote_listener.dart b/lib/src/runner/remote_listener.dart
index 5271f6ed5..883101fa4 100644
--- a/lib/src/runner/remote_listener.dart
+++ b/lib/src/runner/remote_listener.dart
@@ -73,15 +73,13 @@ class RemoteListener {
       }
 
       var message = await channel.stream.first;
-      var platforms = message['testPlatforms']
-          .map((platform) => new TestPlatform.deserialize(platform))
-          .toList();
 
       if (message['asciiGlyphs'] ?? false) glyph.ascii = true;
       var metadata = new Metadata.deserialize(message['metadata']);
       verboseChain = metadata.verboseTrace;
-      var declarer = new Declarer(platforms,
+      var declarer = new Declarer(
           metadata: metadata,
+          platformVariables: message['platformVariables'].toSet(),
           collectTraces: message['collectTraces'],
           noRetry: message['noRetry']);
 
@@ -92,12 +90,13 @@ class RemoteListener {
 
       await declarer.declare(main);
 
-      var os =
-          message['os'] == null ? null : OperatingSystem.find(message['os']);
-      var platform = platforms
-          .firstWhere((platform) => platform.identifier == message['platform']);
       var suite = new Suite(declarer.build(),
-          platform: platform, os: os, path: message['path']);
+          platform: new TestPlatform.deserialize(message['platform']),
+          os: message['os'] == null
+              ? null
+              : OperatingSystem.find(message['os']),
+          path: message['path']);
+
       new RemoteListener._(suite, printZone)._listen(channel);
     }, onError: (error, stackTrace) {
       _sendError(channel, error, stackTrace, verboseChain);
diff --git a/lib/test.dart b/lib/test.dart
index 1ce02c26b..2550bef07 100644
--- a/lib/test.dart
+++ b/lib/test.dart
@@ -53,7 +53,7 @@ Declarer get _declarer {
   // In order to run the tests, we set up our own Declarer via
   // [_globalDeclarer], and schedule a microtask to run the tests once they're
   // finished being defined.
-  _globalDeclarer = new Declarer(TestPlatform.builtIn);
+  _globalDeclarer = new Declarer();
   scheduleMicrotask(() async {
     var suite = new RunnerSuite(const PluginEnvironment(),
         SuiteConfiguration.empty, _globalDeclarer.build(),
diff --git a/test/backend/metadata_test.dart b/test/backend/metadata_test.dart
index 60ace938e..35fc9ef18 100644
--- a/test/backend/metadata_test.dart
+++ b/test/backend/metadata_test.dart
@@ -197,25 +197,25 @@ void main() {
   group("validatePlatformSelectors", () {
     test("succeeds if onPlatform uses valid platforms", () {
       new Metadata.parse(onPlatform: {"vm || browser": new Skip()})
-          .validatePlatformSelectors([TestPlatform.vm]);
+          .validatePlatformSelectors(new Set.from(["vm"]));
     });
 
     test("succeeds if testOn uses valid platforms", () {
       new Metadata.parse(testOn: "vm || browser")
-          .validatePlatformSelectors([TestPlatform.vm]);
+          .validatePlatformSelectors(new Set.from(["vm"]));
     });
 
     test("fails if onPlatform uses an invalid platform", () {
       expect(() {
         new Metadata.parse(onPlatform: {"unknown": new Skip()})
-            .validatePlatformSelectors([TestPlatform.vm]);
+            .validatePlatformSelectors(new Set.from(["vm"]));
       }, throwsFormatException);
     });
 
     test("fails if testOn uses an invalid platform", () {
       expect(() {
         new Metadata.parse(testOn: "unknown")
-            .validatePlatformSelectors([TestPlatform.vm]);
+            .validatePlatformSelectors(new Set.from(["vm"]));
       }, throwsFormatException);
     });
   });
diff --git a/test/runner/parse_metadata_test.dart b/test/runner/parse_metadata_test.dart
index e04b3c14e..343307ec9 100644
--- a/test/runner/parse_metadata_test.dart
+++ b/test/runner/parse_metadata_test.dart
@@ -27,21 +27,21 @@ void main() {
 
   test("returns empty metadata for an empty file", () {
     new File(_path).writeAsStringSync("");
-    var metadata = parseMetadata(_path, TestPlatform.builtIn);
+    var metadata = parseMetadata(_path, new Set());
     expect(metadata.testOn, equals(PlatformSelector.all));
     expect(metadata.timeout.scaleFactor, equals(1));
   });
 
   test("ignores irrelevant annotations", () {
     new File(_path).writeAsStringSync("@Fblthp\n@Fblthp.foo\nlibrary foo;");
-    var metadata = parseMetadata(_path, TestPlatform.builtIn);
+    var metadata = parseMetadata(_path, new Set());
     expect(metadata.testOn, equals(PlatformSelector.all));
   });
 
   test("parses a prefixed annotation", () {
     new File(_path).writeAsStringSync("@foo.TestOn('vm')\n"
         "import 'package:test/test.dart' as foo;");
-    var metadata = parseMetadata(_path, TestPlatform.builtIn);
+    var metadata = parseMetadata(_path, new Set());
     expect(metadata.testOn.evaluate(TestPlatform.vm), isTrue);
     expect(metadata.testOn.evaluate(TestPlatform.chrome), isFalse);
   });
@@ -49,61 +49,54 @@ void main() {
   group("@TestOn:", () {
     test("parses a valid annotation", () {
       new File(_path).writeAsStringSync("@TestOn('vm')\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.testOn.evaluate(TestPlatform.vm), isTrue);
       expect(metadata.testOn.evaluate(TestPlatform.chrome), isFalse);
     });
 
     test("ignores a constructor named TestOn", () {
       new File(_path).writeAsStringSync("@foo.TestOn('foo')\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.testOn, equals(PlatformSelector.all));
     });
 
     group("throws an error for", () {
       test("a named constructor", () {
         new File(_path).writeAsStringSync("@TestOn.name('foo')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("no argument list", () {
         new File(_path).writeAsStringSync("@TestOn\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("an empty argument list", () {
         new File(_path).writeAsStringSync("@TestOn()\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a named argument", () {
         new File(_path)
             .writeAsStringSync("@TestOn(expression: 'foo')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple arguments", () {
         new File(_path)
             .writeAsStringSync("@TestOn('foo', 'bar')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-string argument", () {
         new File(_path).writeAsStringSync("@TestOn(123)\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple @TestOns", () {
         new File(_path)
             .writeAsStringSync("@TestOn('foo')\n@TestOn('bar')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
     });
   });
@@ -120,7 +113,7 @@ void main() {
 
 library foo;
 """);
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(
           metadata.timeout.duration,
           equals(new Duration(
@@ -137,7 +130,7 @@ library foo;
 
 library foo;
 """);
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.timeout.scaleFactor, equals(1));
     });
 
@@ -147,7 +140,7 @@ library foo;
 
 library foo;
 """);
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.timeout.scaleFactor, equals(0.5));
     });
 
@@ -157,109 +150,95 @@ library foo;
 
 library foo;
 """);
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.timeout, same(Timeout.none));
     });
 
     test("ignores a constructor named Timeout", () {
       new File(_path).writeAsStringSync("@foo.Timeout('foo')\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.timeout.scaleFactor, equals(1));
     });
 
     group("throws an error for", () {
       test("an unknown named constructor", () {
         new File(_path).writeAsStringSync("@Timeout.name('foo')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("no argument list", () {
         new File(_path).writeAsStringSync("@Timeout\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("an empty argument list", () {
         new File(_path).writeAsStringSync("@Timeout()\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("an argument list for Timeout.none", () {
         new File(_path).writeAsStringSync("@Timeout.none()\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a named argument", () {
         new File(_path).writeAsStringSync(
             "@Timeout(duration: const Duration(seconds: 1))\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple arguments", () {
         new File(_path)
             .writeAsStringSync("@Timeout.factor(1, 2)\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-Duration argument", () {
         new File(_path).writeAsStringSync("@Timeout(10)\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-num argument", () {
         new File(_path)
             .writeAsStringSync("@Timeout.factor('foo')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple @Timeouts", () {
         new File(_path).writeAsStringSync(
             "@Timeout.factor(1)\n@Timeout.factor(2)\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       group("a Duration with", () {
         test("a non-const constructor", () {
           new File(_path)
               .writeAsStringSync("@Timeout(new Duration(1))\nlibrary foo;");
-          expect(() => parseMetadata(_path, TestPlatform.builtIn),
-              throwsFormatException);
+          expect(() => parseMetadata(_path, new Set()), throwsFormatException);
         });
 
         test("a named constructor", () {
           new File(_path).writeAsStringSync(
               "@Timeout(const Duration.name(seconds: 1))\nlibrary foo;");
-          expect(() => parseMetadata(_path, TestPlatform.builtIn),
-              throwsFormatException);
+          expect(() => parseMetadata(_path, new Set()), throwsFormatException);
         });
 
         test("a positional argument", () {
           new File(_path)
               .writeAsStringSync("@Timeout(const Duration(1))\nlibrary foo;");
-          expect(() => parseMetadata(_path, TestPlatform.builtIn),
-              throwsFormatException);
+          expect(() => parseMetadata(_path, new Set()), throwsFormatException);
         });
 
         test("an unknown named argument", () {
           new File(_path).writeAsStringSync(
               "@Timeout(const Duration(name: 1))\nlibrary foo;");
-          expect(() => parseMetadata(_path, TestPlatform.builtIn),
-              throwsFormatException);
+          expect(() => parseMetadata(_path, new Set()), throwsFormatException);
         });
 
         test("a duplicate named argument", () {
           new File(_path).writeAsStringSync(
               "@Timeout(const Duration(seconds: 1, seconds: 1))\nlibrary foo;");
-          expect(() => parseMetadata(_path, TestPlatform.builtIn),
-              throwsFormatException);
+          expect(() => parseMetadata(_path, new Set()), throwsFormatException);
         });
       });
     });
@@ -268,60 +247,54 @@ library foo;
   group("@Skip:", () {
     test("parses a valid annotation", () {
       new File(_path).writeAsStringSync("@Skip()\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.skip, isTrue);
       expect(metadata.skipReason, isNull);
     });
 
     test("parses a valid annotation with a reason", () {
       new File(_path).writeAsStringSync("@Skip('reason')\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.skip, isTrue);
       expect(metadata.skipReason, equals('reason'));
     });
 
     test("ignores a constructor named Skip", () {
       new File(_path).writeAsStringSync("@foo.Skip('foo')\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.skip, isFalse);
     });
 
     group("throws an error for", () {
       test("a named constructor", () {
         new File(_path).writeAsStringSync("@Skip.name('foo')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("no argument list", () {
         new File(_path).writeAsStringSync("@Skip\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a named argument", () {
         new File(_path).writeAsStringSync("@Skip(reason: 'foo')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple arguments", () {
         new File(_path).writeAsStringSync("@Skip('foo', 'bar')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-string argument", () {
         new File(_path).writeAsStringSync("@Skip(123)\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple @Skips", () {
         new File(_path)
             .writeAsStringSync("@Skip('foo')\n@Skip('bar')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
     });
   });
@@ -329,13 +302,13 @@ library foo;
   group("@Tags:", () {
     test("parses a valid annotation", () {
       new File(_path).writeAsStringSync("@Tags(const ['a'])\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.tags, equals(["a"]));
     });
 
     test("ignores a constructor named Tags", () {
       new File(_path).writeAsStringSync("@foo.Tags(const ['a'])\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.tags, isEmpty);
     });
 
@@ -343,40 +316,34 @@ library foo;
       test("a named constructor", () {
         new File(_path)
             .writeAsStringSync("@Tags.name(const ['a'])\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("no argument list", () {
         new File(_path).writeAsStringSync("@Tags\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a named argument", () {
         new File(_path).writeAsStringSync("@Tags(tags: ['a'])\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple arguments", () {
         new File(_path)
             .writeAsStringSync("@Tags(const ['a'], ['b'])\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-list argument", () {
         new File(_path).writeAsStringSync("@Tags('a')\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple @Tags", () {
         new File(_path).writeAsStringSync(
             "@Tags(const ['a'])\n@Tags(const ['b'])\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
     });
   });
@@ -389,7 +356,7 @@ library foo;
   'vm': const [const Skip(), const Timeout.factor(3)]
 })
 library foo;""");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
 
       var key = metadata.onPlatform.keys.first;
       expect(key.evaluate(TestPlatform.chrome), isTrue);
@@ -407,7 +374,7 @@ library foo;""");
 
     test("ignores a constructor named OnPlatform", () {
       new File(_path).writeAsStringSync("@foo.OnPlatform('foo')\nlibrary foo;");
-      var metadata = parseMetadata(_path, TestPlatform.builtIn);
+      var metadata = parseMetadata(_path, new Set());
       expect(metadata.testOn, equals(PlatformSelector.all));
     });
 
@@ -415,82 +382,70 @@ library foo;""");
       test("a named constructor", () {
         new File(_path)
             .writeAsStringSync("@OnPlatform.name(const {})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("no argument list", () {
         new File(_path).writeAsStringSync("@OnPlatform\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("an empty argument list", () {
         new File(_path).writeAsStringSync("@OnPlatform()\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a named argument", () {
         new File(_path)
             .writeAsStringSync("@OnPlatform(map: const {})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple arguments", () {
         new File(_path)
             .writeAsStringSync("@OnPlatform(const {}, const {})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-map argument", () {
         new File(_path)
             .writeAsStringSync("@OnPlatform(const Skip())\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a non-const map", () {
         new File(_path).writeAsStringSync("@OnPlatform({})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a map with a non-String key", () {
         new File(_path).writeAsStringSync(
             "@OnPlatform(const {1: const Skip()})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a map with a unparseable key", () {
         new File(_path).writeAsStringSync(
             "@OnPlatform(const {'invalid': const Skip()})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a map with an invalid value", () {
         new File(_path).writeAsStringSync(
             "@OnPlatform(const {'vm': const TestOn('vm')})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("a map with an invalid value in a list", () {
         new File(_path).writeAsStringSync(
             "@OnPlatform(const {'vm': [const TestOn('vm')]})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
 
       test("multiple @OnPlatforms", () {
         new File(_path).writeAsStringSync(
             "@OnPlatform(const {})\n@OnPlatform(const {})\nlibrary foo;");
-        expect(() => parseMetadata(_path, TestPlatform.builtIn),
-            throwsFormatException);
+        expect(() => parseMetadata(_path, new Set()), throwsFormatException);
       });
     });
   });
diff --git a/test/utils.dart b/test/utils.dart
index c33b5e86b..c2b062a3e 100644
--- a/test/utils.dart
+++ b/test/utils.dart
@@ -13,7 +13,6 @@ import 'package:test/src/backend/live_test.dart';
 import 'package:test/src/backend/metadata.dart';
 import 'package:test/src/backend/state.dart';
 import 'package:test/src/backend/suite.dart';
-import 'package:test/src/backend/test_platform.dart';
 import 'package:test/src/runner/application_exception.dart';
 import 'package:test/src/runner/configuration/suite.dart';
 import 'package:test/src/runner/engine.dart';
@@ -320,13 +319,13 @@ Future expectTestsPass(void body()) async {
 
 /// Runs [body] with a declarer and returns the declared entries.
 List<GroupEntry> declare(void body()) {
-  var declarer = new Declarer(TestPlatform.builtIn)..declare(body);
+  var declarer = new Declarer()..declare(body);
   return declarer.build().entries;
 }
 
 /// Runs [body] with a declarer and returns an engine that runs those tests.
 Engine declareEngine(void body(), {bool runSkipped: false}) {
-  var declarer = new Declarer(TestPlatform.builtIn)..declare(body);
+  var declarer = new Declarer()..declare(body);
   return new Engine.withSuites([
     new RunnerSuite(const PluginEnvironment(),
         new SuiteConfiguration(runSkipped: runSkipped), declarer.build())