'should filter out lines using filter_fn and set counters properly
based on filter'

def test_filter_fn(self):

    def filter_ts(string):
        if string.lower().startswith('t'):
            return None
        return string
    (contents, provider, data) = self.contents_provider_and_data(filter_fn=filter_ts)
    self.assertEqual(data, [['One'], ['ABCD'], ['ABCD'], ['EFGH']])
    self.assertCounters(provider, 4, 4, 4)
