anchor.diff:    group('Sdk extensions', () {
       StringSink savedOutSink, savedErrorSink;
       int savedExitCode;
  +    ExitHandler savedExitHandler;
   
       setUp(() {
         savedOutSink = outSink;
         savedErrorSink = errorSink;
  +      savedExitHandler = exitHandler;
         savedExitCode = exitCode;
  +      exitHandler = (code) => exitCode = code;
         outSink = new StringBuffer();
         errorSink = new StringBuffer();
       });
  
positive.code: 
  import 'package:analyzer/src/generated/sdk_io.dart';
  import 'package:analyzer_cli/src/driver.dart' show Driver, errorSink, outSink;
  import 'package:path/path.dart' as path;
  import 'package:unittest/unittest.dart';
  
  
negative.code:       outSink = savedOutSink;
        errorSink = savedErrorSink;
        exitCode = savedExitCode;
        exitHandler = savedExitHandler;
      });
  
      test('.packages file present', () async {
        String testDir = path.join(testDirectory, 'data', 'packages_file');
        Driver driver = new Driver()
          ..start([
            '--packages',
            path.join(testDir, '.packages'),
            path.join(testDir, 'sdk_ext_user.dart')
          ]);
  
        DirectoryBasedDartSdk sdk = driver.sdk;
        expect(sdk.useSummary, isFalse);
  