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:unittest/unittest.dart";
+import "package:test/test.dart";
 
-test(int milliseconds) {
+sleepTest(int milliseconds) {
   var watch = new Stopwatch();
   watch.start();
   sleep(new Duration(milliseconds: milliseconds));
   watch.stop();
   expect(watch.elapsedMilliseconds, greaterThanOrEqualTo(milliseconds));
 }
 
 main() {
-  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);
+  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);
+  });
 }