How to use the graphviz.files.Source function in graphviz

def test_save(mocker, py2, filename='nonfilename', directory='nondirectory'):
    source = Source(**SOURCE)
    makedirs = mocker.patch('os.makedirs', autospec=True)
    open_ = mocker.patch('io.open', mocker.mock_open())

    assert source.save(filename, directory) == source.filepath

    assert source.filename == filename and source.directory == directory
    if py2:
        makedirs.assert_called_once_with(source.directory, 0o777)
    else:
        makedirs.assert_called_once_with(source.directory, 0o777, exist_ok=True)
    open_.assert_called_once_with(source.filepath, 'w',
                                  encoding=source.encoding)
    assert open_.return_value.write.call_args_list == [mocker.call(source.source),
                                                       mocker.call(u'\n')]

def source():
    return Source(**SOURCE)

self.assertTrue(isinstance(model.tree(2, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(3, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(4, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(5, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(6, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(7, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(8, 'cancer'), str))
        self.assertTrue(isinstance(model.tree(9, 'cancer'), str))
        self.assertTrue('cancer' in model.tree(0, 'cancer'))

        # Can the tree be converted to an image?
        #import graphviz
        self.assertTrue(isinstance(model.tree(0, 'cancer', image=True), graphviz.files.Source))
        self.assertTrue(isinstance(model.tree(1, 'cancer', image=True), graphviz.files.Source))
        self.assertTrue(isinstance(model.tree(2, 'cancer', image=True), graphviz.files.Source))
        self.assertTrue(isinstance(model.tree(3, 'cancer', image=True), graphviz.files.Source))
        self.assertTrue(isinstance(model.tree(9, 'cancer', image=True), graphviz.files.Source))

        # Does training time return either a float or an int?
        self.assertTrue(isinstance(model.traintime(), float))
        self.assertEqual(model._training_time_to_float(['1', 'milliseconds']), 0.001)
        self.assertEqual(model._training_time_to_float(['1', 'days', '981', 'milliseconds']), 86400.981)
        self.assertEqual(model._training_time_to_float(['2', 'hours', '1', 'minutes', '25', 'seconds', '120', 'milliseconds']), 7285.12)

def test_init_filename():
    assert Source('').filename == 'Source.gv'
    assert type('Named', (Source,), {'name': 'name'})('').filename == 'name.gv'

def __init__(self, source, filename=None, directory=None,
                 format=None, engine=None, encoding=ENCODING):
        super(Source, self).__init__(filename, directory,
                                     format, engine, encoding)
        self.source = source  #: The verbatim DOT source code string.