Add "allowedExtensions" to Transformer.

pkg/barback/test/transformer_test.dart

Index: pkg/barback/test/transformer_test.dart
diff --git a/pkg/barback/test/transformer_test.dart b/pkg/barback/test/transformer_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..9df3f4ab6bd72ed3c7824d5472569788c0acc5ed
--- /dev/null
+++ b/pkg/barback/test/transformer_test.dart
@@ -0,0 +1,59 @@
+// Copyright (c) 2013, 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.
+
+library barback.test.transformer_test;
+
+import 'dart:async';
+
+import 'package:barback/barback.dart';
+import 'package:unittest/unittest.dart';
+
+import 'utils.dart';
+
+main() {
+  initConfig();
+
+  group("isPrimary", () {
+    test("defaults to allowedExtensions", () {
+      var transformer = new ExtensionTransformer(".txt .bin");
+      expect(transformer.isPrimary(makeAsset("foo.txt")),
+          completion(isTrue));
+
+      expect(transformer.isPrimary(makeAsset("foo.bin")),
+          completion(isTrue));
+
+      expect(transformer.isPrimary(makeAsset("foo.nottxt")),
+          completion(isFalse));
+    });
+
+    test("allows all files if allowedExtensions is not overridden", () {
+      var transformer = new MockTransformer();
+      expect(transformer.isPrimary(makeAsset("foo.txt")),
+          completion(isTrue));
+
+      expect(transformer.isPrimary(makeAsset("foo.bin")),
+          completion(isTrue));
+
+      expect(transformer.isPrimary(makeAsset("anything")),
+          completion(isTrue));
+    });
+  });
+}
+
+Asset makeAsset(String path) =>
+    new Asset.fromString(new AssetId.parse("app|$path"), "");
+
+class MockTransformer extends Transformer {
+  MockTransformer();
+
+  Future apply(Transform transform) => new Future.value();
+}
+
+class ExtensionTransformer extends Transformer {
+  final String allowedExtensions;
+
+  ExtensionTransformer(this.allowedExtensions);
+
+  Future apply(Transform transform) => new Future.value();
+}