def METHOD_NAME():
    """Test the ``get_datetime_format``.
    Setup:
        - string value representing datetime.
        - list of values with a datetime.
        - series with a datetime.
    Output:
        - The expected output is the format of the datetime representation.
    """
    # Setup
    string_value = '2021-02-02'
    list_value = [np.nan, '2021-02-02']
    series_value = pd.Series(['2021-02-02T12:10:59'])
    # Run
    string_out = get_datetime_format(string_value)
    list_out = get_datetime_format(list_value)
    series_out = get_datetime_format(series_value)
    # Assert
    expected_output = '%Y-%m-%d'
    assert string_out == expected_output
    assert list_out == expected_output
    assert series_out == '%Y-%m-%dT%H:%M:%S'