It isn't coupling low level implementation details, it is writing tests based on input and output of the unit under test.

The expected output from a unit, given an input is not an implementation detail, unless you have some very different definition of implementation detail than I.

Testing the unit under test produces the expected outputs from a set of inputs implies nothing about implementation details at all. It is also a concept older than dirt:

https://www.researchgate.net/publication/221329933_Iterative...

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MoreQARespect 4 days ago | parent [-]

If the "unit under test" is low level then thats coupling low level implementation details to the test.

If you're vague about what constitutes a "unit" that means youre probably not thinking about this problem.

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nyrikki 4 days ago | parent [-]

Often, even outside of software, unit testing means testing a component's (unit‘s) external behavior.

If you don't accept that concept I can see how TDD and testing in general would be challenging.

I general it is most productive when building competency with a new subject to accept the author's definitions, then adjust once you have experience.

IMHO, the sizing of components is context, language, and team dependent. But it really doesn't matter TDD is just as much about helping with other problems like action bias, and is only one part of a comprehensive testing strategy.

While how you choose to define a 'unit' will impact outcomes, TDD it self isn't dependent on a firm definition.

	▲	MoreQARespect 4 days ago \| parent [-]
		>If you don't accept that concept Nobody anywhere in the world disputes that unit tests should surround a unit. >IMHO, the sizing of components is context, language, and team dependent. But it really doesn't matter Yeah, thats the attitude that will trip you up. The process you use to determine the borders which you will couple to your test - i.e what constitutes a "unit" to be tested is critically important and nonobvious.