Refactor Tests: Replace logmock with self.assertLogs

[FabioRosado]

Last year I needed to figure out how to assert if a logging level was called. I tried a few things and came up with the solution to mock the _LOGGER.<level> and then assert if logmock was called.

I have noticed that you can use a self.assertLogs(self, logger, level) to check if a message was logged. Since when we are testing we don't really care about what message was logged but if the message was logging we should replace every amock.patch('opsdroid.core._LOGGER.exception') as logmock with the self.assertLogs.

This should make the tests a bit more readable and easier to maintain in the future. This Issue is also great for new contributors since it's quite easy to implement.

For a better explanation check the example:

Old style: test_main.py:132-136

    def test_welcome_message(self):
        config = {"welcome-message": True}
        with mock.patch('opsdroid.__main__._LOGGER.info') as logmock:
            opsdroid.welcome_message(config)
            self.assertTrue(logmock.called)

Refactored test

    def test_welcome_message(self):
        config = {"welcome-message": True}
        opsdroid.welcome_message(config)
        self.assertLogs('_LOGGER', 'info')

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[jacobtomlinson]

Awesome! Looks like this was added to unittests in 3.4 (back in Feb).