def test_input_loop_with_null_default_value(mock_prompt) -> None:
    """Test `Prompt.ask` is run repeatedly until a valid answer is provided.

    Test for `default_value` parameter equal to None.
    """
    # Simulate user providing None input initially and then a valid input
    mock_prompt.side_effect = [None, DEFAULT]

    assert read_user_variable(VARIABLE, None) == DEFAULT
    assert mock_prompt.call_count == 2
Test `Prompt.ask` is run repeatedly until a valid answer is provided.

    Test for `default_value` parameter equal to None.
    
tests/test_read_user_variable.py