def _tester(func, *args):
    """
    Tests function ``func`` on arguments and returns first positive.

    >>> _tester(lambda x: x%3 == 0, 1, 2, 3, 4, 5, 6)
    3
    >>> _tester(lambda x: x%3 == 0, 1, 2)
    None

    :param func: function(arg)->boolean
    :param args: other arguments
    :return: something or none
    """
    for arg in args:
        if arg is not None and func(arg):
            return arg

    return None