pkg/unittest: Run tests in zones

pkg/unittest/lib/src/spread_args_helper.dart

 part of unittest;
 
 /** Simulates spread arguments using named arguments. */
 // TODO(sigmund): remove this class and simply use a closure with named
 // arguments (if still applicable).
 class _SpreadArgsHelper {
   final Function callback;
   final int minExpectedCalls;
   final int maxExpectedCalls;
   final Function isDone;
@@ skipping 101 matching lines @@
 
   invoke2(arg1, arg2) {
     return _guardAsync(
         () {
           if (shouldCallBack()) {
             return callback(arg1, arg2);
           }
         },
         after, testCase);
   }
+
+  _guardAsync(Function tryBody, Function finallyBody, TestCase testCase) {
+    assert(testCase != null);
+    try {
+      return tryBody();
+    } catch (e, trace) {
+      _registerException(testCase, e, trace);
+    } finally {
+      if (finallyBody != null) finallyBody();
+    }
+  }
 }