Fix test_flooding_prevention() when run from tox

    def test_flooding_prevention(sentry_init_custom):
        """Ensure that an infinite synchronization due to a unhandled error
        will not explode the Sentry quota.
        """
    
        def whoopsy():
            """Problematic function ... """
            try:
                raise ValueError("Mock'ed error")
            except Exception:
                capture_exception()
    
        def whoopsy2():
            """Problematic function ... """
            try:
                raise ValueError("Mock'ed error")
            except Exception:
                capture_exception()
    
        sentry_init_custom(before_send=nxdrive.tracing.before_send)
    
        # Ensure there is no event by default
        assert not nxdrive.tracing._EVENTS
    
        # The first event of an error should be sent
        whoopsy()
>       assert len(nxdrive.tracing._EVENTS) == 1
E       AssertionError: assert 0 == 1