<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def find_top_level_directory(start_directory):
 """Finds the top-level directory of a project given a start directory inside the project. Parameters start_directory : str The directory in which test discovery will start. """

    top_level = start_directory
    while os.path.isfile(os.path.join(top_level, '__init__.py')):
        top_level = os.path.dirname(top_level)
        if top_level == os.path.dirname(top_level):
            raise ValueError("Can't find top level directory")
    return os.path.abspath(top_level)