def METHOD_NAME(self):
    c = self.c
    u = c.undoer
    x = GitDiffController(c=c)
    # Setup the outline.
    root = c.rootPosition()
    while root.hasNext():
        root.next().doDelete()
    c.selectPosition(root)
    # Run the command.
    expected_last_headline = 'git diff revs: HEAD'
    try:
        sys.stdout = open(os.devnull, 'w')
        x.diff_two_revs()
    finally:
        sys.stdout = sys.__stdout__
    # #3497: Silently skip the test if nothing has changed.
    if c.lastTopLevel() == root:
        return
    self.assertEqual(c.lastTopLevel().h.strip(), expected_last_headline)
    # Test undo/redo.
    u.undo()
    self.assertEqual(c.lastTopLevel(), root)
    u.redo()
    self.assertEqual(c.lastTopLevel().h.strip(), expected_last_headline)