Fix to workaround non-propagation of exception stack-traces by dartc.

client/testing/unittest/shared.dart

 // Copyright (c) 2011, 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.
 
 /**
  * Description text of the current test group. If multiple groups are nested,
  * this will contain all of their text concatenated.
  */
 String _currentGroup = '';
 
@@ skipping 141 matching lines @@
 
   _platformDefer(() {
     assert (_currentTest == 0);
     _nextBatch();
   });
 }
 
 /** Runs a single test. */
 _runTest(TestCase testCase) {
   try {
-    // TODO(sigmund): remove this declaration once dartc supports trapping error
-    // traces.
-    var trace = '';
     _callbacksCalled = 0;
     _state = _RUNNING_TEST;
 
     testCase.test();
 
     if (_state != _UNCAUGHT_ERROR) {
       if (testCase.callbacks == _callbacksCalled) {
         testCase.pass();
       }
     }
 
   } catch (ExpectException e, var trace) {
     if (_state != _UNCAUGHT_ERROR) {
-      testCase.fail(e.message, trace.toString());
+      //TODO(pquitslund) remove guard once dartc reliably propagates traces
+      testCase.fail(e.message, trace == null ? '' : trace.toString());
     }
   } catch (var e, var trace) {
     if (_state != _UNCAUGHT_ERROR) {
-      testCase.error('Caught ${e}', trace.toString());
+      //TODO(pquitslund) remove guard once dartc reliably propagates traces
+      testCase.error('Caught ${e}', trace == null ? '' : trace.toString());
     }
   } finally {
     _state = _READY;
   }
 }
 
 /**
  * Runs a batch of tests, yielding whenever an asynchronous test starts
  * running. Tests will resume executing when such asynchronous test calls
  * [done] or if it fails with an exception.
@@ skipping 151 matching lines @@
   }
 
   void error(String message, String stackTrace) {
     result = _ERROR;
     this.message = message;
     this.stackTrace = stackTrace;
   }
 }
 
 typedef void TestFunction();