TestCase times out after 20 seconds.

dart/pkg/unittest/lib/unittest.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.
 
 /**
  * A library for writing dart unit tests.
  *
  * ## Installing ##
  *
  * Use [pub][] to install this package. Add the following to your `pubspec.yaml`
@@ skipping 734 matching lines @@
 
 /**
  * Runs the next test.
  */
 void _runTest() {
   if (_currentTestCaseIndex >= testCases.length) {
     _completeTests();
   } else {
     final testCase = testCases[_currentTestCaseIndex];
     var f = _guardAsync(testCase._run, null, testCase);
+    Timer timer;
+    try {
+      final Duration timeout = unittestConfiguration.timeout;
+      timer = new Timer(timeout, () {
+        testCase.error("Test timed out after ${timeout.inSeconds} seconds.");
+      });
+    } on UnsupportedError catch (e) {
+      if (e.message != "Timer greater than 0.") rethrow;
+      // Support running on d8 and jsshell which don't support timers.
+    }
     f.whenComplete(() {
+      if (timer != null) timer.cancel();
       var now = new DateTime.now().millisecondsSinceEpoch;
       if ((now - _lastBreath) >= BREATH_INTERVAL) {
         _lastBreath = now;
         Timer.run(_nextTestCase);
       } else {
         runAsync(_nextTestCase); // Schedule the next test.
       }
     });
   }
 }
@@ skipping 100 matching lines @@
 
   if (!formatStacks) return trace;
 
   // Format the stack trace by removing everything above TestCase._runTest,
   // which is usually going to be irrelevant. Also fold together unittest and
   // core library calls so only the function the user called is visible.
   return new Trace(trace.frames.takeWhile((frame) {
     return frame.package != 'unittest' || frame.member != 'TestCase._runTest';
   })).terse.foldFrames((frame) => frame.package == 'unittest' || frame.isCore);
 }