def METHOD_NAME(self):
    import sys
    existing_file = sys.executable
    result = examinee.existing_file(existing_file)
    self.assertEqual(existing_file, result)
    with capture_out() as (stdout, stderr):
        with self.assertRaises(Failure):
            examinee.existing_file('no such file, I hope')
    self.assertIn('not an existing file', stderr.getvalue().strip())
    self.assertTrue(len(stdout.getvalue()) == 0)
    # should also work with pathlib.Path
    existing_file = pathlib.Path(existing_file)
    self.assertEqual(examinee.existing_file(existing_file), existing_file)