implement dirty checking for @observable objects

pkg/observe/test/observe_test_utils.dart

+// 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 observe.test.observe_test_utils;
+
+import 'dart:async';
+import 'package:observe/observe.dart';
+import 'package:unittest/unittest.dart';
+
+// TODO(jmesserly): use matchers when we have a way to compare ChangeRecords.
+// For now just use the toString.
+expectChanges(actual, expected, {reason}) =>
+    expect('$actual', '$expected', reason: reason);
+
+/**
+ * This change pumps events relevant to observers and data-binding tests.
+ * This must be used inside an [observeTest].
+ *
+ * Executes all pending [runAsync] calls on the event loop, as well as
+ * performing [Observable.dirtyCheck], until there are no more pending events.
+ * It will always dirty check at least once.
+ */
+void performMicrotaskCheckpoint() {
+  Observable.dirtyCheck();
+
+  while (_pending.length > 0) {
+    var pending = _pending;
+    _pending = [];
+
+    for (var callback in pending) {
+      try {
+        callback();
+      } catch (e, s) {
+        new Completer().completeError(e, s);
+      }
+    }
+
+    Observable.dirtyCheck();
+  }
+}
+
+List<Function> _pending = [];
+
+/**
+ * Wraps the [testCase] in a zone that supports [performMicrotaskCheckpoint],
+ * and returns the test case.
+ */
+wrapMicrotask(void testCase()) {
+  return () {
+    runZonedExperimental(() {
+      try {
+        testCase();
+      } finally {
+        performMicrotaskCheckpoint();
+      }
+    }, onRunAsync: (callback) => _pending.add(callback));
+  };
+}
+
+/**
+ * This is a special kind of unit [test], that supports
+ * calling [performMicrotaskCheckpoint] during the test to pump events
+ * that original from observable objects.
+ */
+observeTest(name, testCase) => test(name, wrapMicrotask(testCase));
+
+/** The [solo_test] version of [observeTest]. */
+solo_observeTest(name, testCase) => solo_test(name, wrapMicrotask(testCase));