Get rid of an unused library.

test/runner/engine_test.dart

 // Copyright (c) 2015, 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.
 
 import 'package:test/src/backend/group.dart';
 import 'package:test/src/backend/state.dart';
-import 'package:test/src/backend/test.dart';
 import 'package:test/src/runner/engine.dart';
 import 'package:test/src/runner/runner_suite.dart';
 import 'package:test/src/runner/vm/environment.dart';
 import 'package:test/test.dart';
 
 import '../utils.dart';
 
 void main() {
   test("runs each test in each suite in order", () async {
     var testsRun = 0;
@@ skipping 128 matching lines @@
           first = false;
         }, count: 2));
 
         expect(liveTest.onComplete, completes);
       }));
 
       return engine.run();
     });
   });
 }