Switch analysis_server to use 'package:test'.

pkg/analysis_server/test/edit/assists_test.dart

 // Copyright (c) 2014, 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.
 
 library test.edit.assists;
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/edit/edit_domain.dart';
 import 'package:plugin/manager.dart';
+import 'package:test/test.dart';
 import 'package:test_reflective_loader/test_reflective_loader.dart';
-import 'package:unittest/unittest.dart' hide ERROR;
 
 import '../analysis_abstract.dart';
 import '../utils.dart';
 
 main() {
   initializeTestEnvironment();
-  defineReflectiveTests(AssistsTest);
+  defineReflectiveSuite(() {
+    defineReflectiveTests(AssistsTest);
+  });
 }
 
 @reflectiveTest
 class AssistsTest extends AbstractAnalysisTest {
   List<SourceChange> changes;
 
   prepareAssists(String search, [int length = 0]) async {
     int offset = findOffset(search);
     await prepareAssistsAt(offset, length);
   }
@@ skipping 78 matching lines @@
       if (change.message == message) {
         String resultCode =
             SourceEdit.applySequence(testCode, change.edits[0].edits);
         expect(resultCode, expectedCode);
         return;
       }
     }
     fail("Expected to find |$message| in\n" + changes.join('\n'));
   }
 }