# Source code for txaio.testutil

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    import txaio
    from contextlib import contextmanager

    @contextmanager
    def replace_loop(new_loop):
        """
        This is a context-manager that sets the txaio event-loop to the
        one supplied temporarily. It's up to you to ensure you pass an
        event_loop or a reactor instance depending upon asyncio/Twisted.

        Use like so:

        .. sourcecode:: python

            from twisted.internet import task
            with replace_loop(task.Clock()) as fake_reactor:
                f = txaio.call_later(5, foo)
                fake_reactor.advance(10)
                # ...etc
        """

        # setup
        orig = txaio.config.loop
        txaio.config.loop = new_loop

        yield new_loop

        # cleanup
        txaio.config.loop = orig