def test_can_save_as_xyz(self, mock_open, mock_string):
open_return = MagicMock()
mock_file = Mock()
mock_write = MagicMock()
mock_file.write = mock_write
open_return.__enter__.return_value = mock_file
mock_open.return_value = open_return
f = File()
f.save("/path/file.xyz")
mock_string.assert_called_with(f)
mock_open.assert_called_once_with("/path/file.xyz", "w")
mock_write.assert_called_with(mock_string.return_value)
def test_unknown_file_extension(self):
f = File()
with self.assertRaises(ValueError):
f.save("/path/file.abc")
