def test_must_work_with_stdin(self, filename, click_mock): event_data = "some data" # Mock file pointer fp_mock = Mock() # Mock the context manager click_mock.open_file.return_value.__enter__.return_value = fp_mock fp_mock.read.return_value = event_data result = invoke_cli_get_event(filename) self.assertEquals(result, event_data) fp_mock.read.assert_called_with()