Added the ability to filter which tests are run by name, using a --filter

lib/unittest/config.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.
 
 /** This file is sourced by unitest.dart. */
 
 /**
  * Hooks to configure the unittest library for different platforms. This class
  * implements the API in a platform-independent way. Tests that want to take
  * advantage of the platform can create a subclass and override methods from
@@ skipping 43 matching lines @@
       }
     }
 
     // Show the summary.
     print('');
 
     var success = false;
     if (passed == 0 && failed == 0 && errors == 0) {
       print('No tests found.');
       // This is considered a failure too: if this happens you probably have a
-      // bug in your unit tests.
+      // bug in your unit tests, unless you are filtering.
+      if (getFilter() != null) {
+        success = true;
+      }
     } else if (failed == 0 && errors == 0 && uncaughtError == null) {
       print('All $passed tests passed.');
       success = true;
     } else {
       if (uncaughtError != null) {
         print('Top-level uncaught error: $uncaughtError');
       }
       print('$passed PASSED, $failed FAILED, $errors ERRORS');
     }
 
     // An exception is used by the test infrastructure to detect failure.
     if (!success) throw new Exception("Some tests failed.");
   }
 
   String _indent(String str) {
     // TODO(nweiz): Use this simpler code once issue 2980 is fixed.
     // return str.replaceAll(const RegExp("^", multiLine: true), "  ");
 
     return Strings.join(str.split("\n").map((line) => "  $line"), "\n");
   }
 }