Fix fail call.

pkg/unittest/unittest.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.
 
 /**
  * A library for writing dart unit tests.
  *
  * To import this library, specify the relative path to
  * pkg/unittest/unittest.dart.
  *
@@ skipping 220 matching lines @@
   } catch (e) {
     threw = true;
 
     // Also let the callback look at it.
     if (callback != null) {
       var result = callback(e);
 
       // If the callback explicitly returned false, treat that like an
       // expectation too. (If it returns null, though, don't.)
       if (result == false) {
-        _fail('Exception:\n$e\ndid not match expectation.');
+        fail('Exception:\n$e\ndid not match expectation.');
       }
     }
   }
 
-  if (threw != true) _fail('An expected exception was not thrown.');
+  if (threw != true) fail('An expected exception was not thrown.');
 }
 
 /**
  * Creates a new test case with the given description and body. The
  * description will include the descriptions of any surrounding group()
  * calls.
  */
 void test(String spec, TestFunction body) {
   ensureInitialized();
   _tests.add(new TestCase(_tests.length + 1, _fullSpec(spec), body, 0));
@@ skipping 614 matching lines @@
 }
 
 /** Enable a test by ID. */
 void enableTest(int testId) => _setTestEnabledState(testId, true);
 
 /** Disable a test by ID. */
 void disableTest(int testId) => _setTestEnabledState(testId, false);
 
 /** Signature for a test function. */
 typedef void TestFunction();