Upgrade to the new test runner.

test/span_scanner_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 string_scanner.span_scanner_test;
 
 import 'package:string_scanner/string_scanner.dart';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 void main() {
   var scanner;
   setUp(() {
     scanner = new SpanScanner('foo\nbar\nbaz', sourceUrl: 'source');
   });
 
   test("tracks the span for the last match", () {
     scanner.scan('fo');
     scanner.scan('o\nba');
@@ skipping 32 matching lines @@
     expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
     expect(span.end.offset, equals(6));
     expect(span.end.line, equals(1));
     expect(span.end.column, equals(2));
     expect(span.start.sourceUrl, equals(Uri.parse('source')));
 
     expect(span.text, equals(''));
   });
 }