Switch analysis_server to use 'package:test'.

pkg/analysis_server/test/source/caching_put_package_map_provider_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.
 
 library test.source.caching_pub_package_map_provider;
 
 import 'dart:convert';
 import 'dart:core';
 import 'dart:io' as io;
 
 import 'package:analysis_server/src/source/caching_pub_package_map_provider.dart';
 import 'package:analyzer/file_system/file_system.dart';
 import 'package:analyzer/file_system/memory_file_system.dart';
 import 'package:analyzer/source/package_map_provider.dart';
 import 'package:analyzer/src/dart/sdk/sdk.dart';
 import 'package:analyzer/src/generated/engine.dart';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 import '../utils.dart';
 
 main() {
   initializeTestEnvironment();
 
   group('CachingPubPackageMapProvider', () {
     MemoryResourceProvider resProvider;
     _MockPubListRunner mockRunner;
     bool writeFileException;
@@ skipping 367 matching lines @@
       provider.newFolder(path);
     }
     int fileCount = _filePaths.length;
     for (int fileIndex = 0; fileIndex < fileCount; ++fileIndex) {
       String path = _filePaths[fileIndex];
       TimestampedData content = _fileContents[fileIndex];
       provider.newFile(path, content.data, content.modificationTime);
     }
   }
 }