mojo: Add RunLoop::Current() and refactor unit tests.

mojo/python/tests/async_wait_unittest.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import unittest
+import mojo_unittest
 
 # pylint: disable=F0401
-import mojo.embedder
 from mojo import system
 
 
-class AsyncWaitTest(unittest.TestCase):
+class AsyncWaitTest(mojo_unittest.MojoTestCase):
 
   def setUp(self):
-    mojo.embedder.Init()
-    self.loop = system.RunLoop()
+    super(AsyncWaitTest, self).setUp()
     self.array = []
     self.handles = system.MessagePipe()
     self.cancel = self.handles.handle0.AsyncWait(system.HANDLE_SIGNAL_READABLE,
                                                  system.DEADLINE_INDEFINITE,
                                                  self._OnResult)
 
   def tearDown(self):
     self.cancel()
     self.handles = None
     self.array = None
-    self.loop = None
+    super(AsyncWaitTest, self).tearDown()
 
   def _OnResult(self, value):
     self.array.append(value)
 
   def _WriteToHandle(self):
     self.handles.handle1.WriteMessage()
 
   def _PostWriteAndRun(self):
     self.loop.PostDelayedTask(self._WriteToHandle, 0)
     self.loop.RunUntilIdle()
 
   def testAsyncWait(self):
     self._PostWriteAndRun()
     self.assertEquals(len(self.array), 1)
     self.assertEquals(system.RESULT_OK, self.array[0])
 
   def testAsyncWaitCancel(self):
     self.loop.PostDelayedTask(self.cancel, 0)
     self._PostWriteAndRun()
     self.assertEquals(len(self.array), 0)
 
   def testAsyncWaitImmediateCancel(self):
     self.cancel()
     self._PostWriteAndRun()
     self.assertEquals(len(self.array), 0)