Adding package:code_transformers for unifying common transformers code

pkg/code_transformers/lib/tests.dart

+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Collection of utilities which are useful for creating unit tests for
+/// Barback transformers.
+library code_transformers.tests;
+
+import 'dart:async' show Future;
+
+import 'package:barback/barback.dart' show Transformer;
+import 'package:unittest/unittest.dart';
+
+import 'src/test_harness.dart';
+
+/// Defines a test which invokes [applyTransformers].
+testPhases(String testName, List<List<Transformer>> phases,
+    Map<String, String> inputs, Map<String, String> results,
+    [List<String> messages]) {
+  test(testName,
+    () => applyTransformers(phases, inputs: inputs, results: results,
+        messages: messages));
+}
+
+/// Updates the provided transformers with [inputs] as asset inputs then
+/// validates that [results] were generated.
+///
+/// The keys for inputs and results are 'package_name|lib/file.dart'.
+/// Only files which are specified in results are validated.
+///
+/// If [messages] is non-null then this will validate that only the specified
+/// messages were generated, ignoring info messages.
+Future applyTransformers(List<List<Transformer>> phases,
+    {Map<String, String> inputs: const {},
+    Map<String, String> results: const {},
+    List<String> messages: const []}) {
+
+  var helper = new TestHelper(phases, inputs, messages)..run();
+  return helper.checkAll(results).then((_) => helper.tearDown());
+}