Your tests are an assertion that 'no matter what this will never change'. If your interface can change then you are testing implementation details instead of the behavior users care about.

the above is really hard. A lot of tdd 'experts' don't understand is and teach fragile tests that are not worth having.

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8note 3 hours ago | parent | next [-]

https://www.hyrumslaw.com/

your implementation is your interface. its a bit naive or hating-your-users to assume your tests are what your users care about. theyre dealing with everything, regardless of what youve tested or not.

	▲	SirSavary 2 hours ago \| parent [-]
		Hyrum's law is about the real consumers/users (inadvertently) depending on any observable behaviour they can get their hands on. TDD/BDD tests are meant to define the intended contract of a system. These are not the same thing.

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switchbak 4 hours ago | parent | prev [-]

Refactoring is changing the design of the code without affecting the behaviour.

You can change an interface and not change the behaviour.

I have rarely heard such a rigid interpretation such as this.