Facade Pattern in Python with Mock Simplification

class SubsystemA:
    def operation_a(self):
        return "Subsystem A: ready"

class SubsystemB:
    def operation_b(self):
        return "Subsystem B: ready"

class SubsystemC:
    def operation_c(self):
        return "Subsystem C: ready"


class Facade:
    def __init__(self):
        self._a = SubsystemA()
        self._b = SubsystemB()
        self._c = SubsystemC()

    def start(self):
        results = [
            self._a.operation_a(),
            self._b.operation_b(),
            self._c.operation_c(),
        ]
        return " | ".join(results)

    def stop(self):
        return "All subsystems stopped"


class MockFacade(Facade):
    def __init__(self, fail=False):
        super().__init__()
        self._fail = fail

    def start(self):
        if self._fail:
            return "Mock: simulation failure"
        return "Mock: " + super().start()


if __name__ == "__main__":
    real = Facade()
    mock = MockFacade()
    mock_fail = MockFacade(fail=True)

    print("Real facade:", real.start())
    print("Mock facade:", mock.start())
    print("Mock failed:", mock_fail.start())
    print("Stop:", real.stop())