def test_makeDirectoryError(self):
        """
        Creating a directory that already exists should fail with a
        C{ftp.FileExistsError}.
        """
        self.createDirectory('foo')
        d = self.shell.makeDirectory(('foo',))
        return self.assertFailure(d, ftp.FileExistsError)

        Creating a directory that already exists should fail with a
        C{ftp.FileExistsError}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_ftp.py