Revert "Remove package:unittest from some tests"

tests/standalone/io/sleep_test.dart

 // Copyright (c) 2013, 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.
 
 import "dart:io";
-import "package:test/test.dart";
+import "package:unittest/unittest.dart";
 
-sleepTest(int milliseconds) {
+test(int milliseconds) {
   var watch = new Stopwatch();
   watch.start();
   sleep(new Duration(milliseconds: milliseconds));
   watch.stop();
   expect(watch.elapsedMilliseconds, greaterThanOrEqualTo(milliseconds));
 }
 
 main() {
-  test("zero", () {
-    sleepTest(0);
-  });
-  test("one", () {
-    sleepTest(1);
-  });
-  test("ten", () {
-    sleepTest(10);
-  });
-  test("100", () {
-    sleepTest(100);
-  });
-  test("error", () {
-    bool sawError = false;
-    try {
-      sleep(new Duration(milliseconds: -1));
-      expect(false, isTrue);  // should not reach here.
-    } on ArgumentError catch(e) {
-      sawError = true;
-    }
-    expect(sawError, isTrue);
-  });
+  test(0);
+  test(1);
+  test(10);
+  test(100);
+  bool sawError = false;
+  try {
+    sleep(new Duration(milliseconds: -1));
+    expect(false, isTrue);  // should not reach here.
+  } on ArgumentError catch(e) {
+    sawError = true;
+  }
+  expect(sawError, isTrue);
 }