Validate that the source directory exists and it contains the user script

    Args:
        script (str):  Script filename.
        directory (str): Directory containing the source file.

    Raises:
        ValueError: If ``directory`` does not exist, is not a directory, or does not contain ``script``.

def validate_source_dir(script, directory):
    """Validate that the source directory exists and it contains the user script

    Args:
        script (str):  Script filename.
        directory (str): Directory containing the source file.

    Raises:
        ValueError: If ``directory`` does not exist, is not a directory, or does not contain ``script``.
    """
    if directory:
        if not os.path.isfile(os.path.join(directory, script)):
            raise ValueError('No file named "{}" was found in directory "{}".'.format(script, directory))

    return True