Refactor the barback tests somewhat.

pkg/barback/test/cancelable_future_test.dart

Index: pkg/barback/test/cancelable_future_test.dart
diff --git a/pkg/barback/test/cancelable_future_test.dart b/pkg/barback/test/cancelable_future_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..d5f9ae43a6851cfcd32c904533c5dd8cf302ace6
--- /dev/null
+++ b/pkg/barback/test/cancelable_future_test.dart
@@ -0,0 +1,62 @@
+// 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.cancelable_future_test;
+
+import 'dart:async';
+
+import 'package:barback/src/cancelable_future.dart';
+import 'package:barback/src/utils.dart';
+import 'package:unittest/unittest.dart';
+
+import 'utils.dart';
+
+main() {
+  initConfig();
+
+  var completer;
+  var future;
+  setUp(() {
+    completer = new Completer();
+    future = new CancelableFuture(completer.future);
+  });
+
+  group("when not canceled", () {
+    test("correctly completes successfully", () {
+      expect(future, completion(equals("success")));
+      completer.complete("success");
+    });
+
+    test("correctly completes with an error", () {
+      expect(future, throwsA(equals("error")));
+      completer.completeError("error");
+    });
+  });
+
+  group("when canceled", () {
+    test("never completes successfully", () {
+      var completed = false;
+      future.whenComplete(() {
+        completed = true;
+      });
+
+      future.cancel();
+      completer.complete("success");
+
+      expect(pumpEventQueue().then((_) => completed), completion(isFalse));
+    });
+
+    test("never completes with an error", () {
+      var completed = false;
+      future.catchError((_) {}).whenComplete(() {
+        completed = true;
+      });
+
+      future.cancel();
+      completer.completeError("error");
+
+      expect(pumpEventQueue().then((_) => completed), completion(isFalse));
+    });
+  });
+}