'Tool dependency definitions can only be invalid if they include a definition for a complex
repository dependency and the repository dependency definition is invalid.  This method
retrieves the error message associated with the invalid tool dependency for display in the
caller.'

def generate_message_for_invalid_tool_dependencies(self, metadata_dict):

    message = ''
    if metadata_dict:
        invalid_tool_dependencies = metadata_dict.get('invalid_tool_dependencies', None)
        if invalid_tool_dependencies:
            for (td_key, requirement_dict) in invalid_tool_dependencies.items():
                error = requirement_dict.get('error', None)
                if error:
                    message = ('%s        ' % str(error))
    return message
