Upgrade unittest to be able to use isNotEmpty.

pkg/analysis_server/test/integration/analysis/update_content_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.integration.analysis.update.content;
 
 import 'package:analysis_server/src/protocol.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../reflective_tests.dart';
 import '../integration_tests.dart';
 
 main() {
   runReflectiveTests(Test);
 }
 
 @ReflectiveTestCase()
 class Test extends AbstractAnalysisServerIntegrationTest {
   test_updateContent() {
     String pathname = sourcePath('test.dart');
     String goodText = r'''
 main() {
   print("Hello, world!");
 }''';
     String badText = goodText.replaceAll(';', '');
     writeFile(pathname, badText);
     standardAnalysisSetup();
     return analysisFinished.then((_) {
       // The contents on disk (badText) are missing a semicolon.
-      expect(currentAnalysisErrors[pathname], isNot(isEmpty));
+      expect(currentAnalysisErrors[pathname], isNotEmpty);
     }).then((_) => sendAnalysisUpdateContent({
       pathname: new AddContentOverlay(goodText)
     })).then((result) => analysisFinished).then((_) {
       // There should be no errors now because the contents on disk have been
       // overriden with goodText.
       expect(currentAnalysisErrors[pathname], isEmpty);
       return sendAnalysisUpdateContent({
         pathname: new ChangeContentOverlay(
             [new SourceEdit(goodText.indexOf(';'), 1, '')])
       });
     }).then((result) => analysisFinished).then((_) {
       // There should be errors now because we've removed the semicolon.
-      expect(currentAnalysisErrors[pathname], isNot(isEmpty));
+      expect(currentAnalysisErrors[pathname], isNotEmpty);
       return sendAnalysisUpdateContent({
         pathname: new ChangeContentOverlay(
             [new SourceEdit(goodText.indexOf(';'), 0, ';')])
       });
     }).then((result) => analysisFinished).then((_) {
       // There should be no errors now because we've added the semicolon back.
       expect(currentAnalysisErrors[pathname], isEmpty);
       return sendAnalysisUpdateContent({
         pathname: new RemoveContentOverlay()
       });
     }).then((result) => analysisFinished).then((_) {
       // Now there should be errors again, because the contents on disk are no
       // longer overridden.
-      expect(currentAnalysisErrors[pathname], isNot(isEmpty));
+      expect(currentAnalysisErrors[pathname], isNotEmpty);
     });
   }
 }