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kotlinlang

Do data classes need unit tests if we know they only have a primary constructor and no methods?

data class(val id: String, val firstName: String, val lastName: String)

That depends entirely on your testing strategy.

It is like `assertEquals(4, 2 + 2)` — sometimes it does make sense, but usually it does not.

I would say that data classes are already covered at many places when testing is concerned

If they have any behavior different from only keeping data, (for instance a static parse or whatever), I'd write a test for them

Not for unit tests. The behavior of the data class is already tested by JB at language/compiler level. Can be tested as part of integration tests