def test_fail_msg(exp, test_name, miner_name, matched=0):
    """
    Formats message string for false test assertion.
        - exp:
            Expected number of events (to be matched).
        - test_name:
            Name of running test.
        - miner_name:
            Name of miner function.
        - matched:
            Number of events matched with miner function.
            By default it's 0.
    """
    return 'Expected to match {} events, not {} in {} with {}.'.format(
        exp, matched, test_name, miner_name)