tests: import unittest via package: url

tests/lib/async/deferred/deferred_in_isolate_test.dart

 import 'dart:isolate';
 import 'dart:async';
-import '../../../../pkg/unittest/lib/unittest.dart';
+import 'package:unittest/unittest.dart';
 
 @a import 'deferred_in_isolate_lib.dart' as lib1;
 @b import 'deferred_api_library.dart' as lib2;
 
 const a = const DeferredLibrary("lib1");
 const b = const DeferredLibrary("NonExistingFile", uri: "wrong/");
 
 loadDeferred(ports) {
   a.load().then((_) {
     ports[0].send(lib1.f());
@@ skipping 11 matching lines @@
     List<ReceivePort> ports = new List.generate(2, (_) => new ReceivePort());
     ports[0].first.then(expectAsync((msg) {
        expect(msg, equals("hi"));
     }));
     ports[1].first.then(expectAsync((msg) {
       expect(msg, equals("Error caught"));
     }));
     Isolate.spawn(loadDeferred, ports.map((p) => p.sendPort).toList());
   });
 }