def METHOD_NAME(self, extends_arg):
    self.call("python -m flow init".split())
    self.call(f"python -m flow template create {extends_arg}".split())
    assert os.path.exists("templates/script.sh")
    with open("templates/script.sh") as fh:
        custom_script_lines = fh.read().splitlines()
    assert '{% extends "slurm.sh" %}' in custom_script_lines[0]