class LogLineBlockTest(unittest.TestCase):
    def setUp(self):
        self.obj = LogLineBlock()

    def test_can_take_initial_list_of_lines(self):
        obj = LogLineBlock([TIME_STEP_START_LINE])
        self.assertEqual(len(obj.lines), 1)

    def test_can_append_new_lines(self):
        self.assertEqual(len(self.obj.lines), 0)
        self.obj.append_line(TIME_STEP_START_LINE)
        self.assertEqual(len(self.obj.lines), 1)

    def test_denies_non_log_lines(self):
        with self.assertRaises(ValueError):
            self.obj.append_line('not a log line')

    def test_has_prop_lines(self):
        self.assertIsInstance(self.obj.lines, list)
 def setUp(self):
     self.obj = LogLineBlock()