Port a core set of unit tests to kotlin

[kevinb9n]

A number of issues mention kotlin: https://github.com/google/truth/issues?q=is%3Aissue+is%3Aopen+kotlin

Before worrying about any of them I think we should have a core set of unit tests ported to Kotlin. These only need to cover varying API shapes, not all variations of behavior. (I'd put this requirement on any library that wants to claim it's for both languages.) Of course, a custom subject or two should be included.

(I might actually be able to take this task, but not promising yet.)

[cpovirk]

This may already be what you have in mind, but I suspect that we'll learn more from (re)writing the tests of a "real" project in Kotlin than from rewriting Truth's own tests in Kotlin. Truth's own tests tend to be weird in a number of ways (example).

Truth will of course still need Kotlin tests (beyond the ones we have for our single (and currently internal-only) Kotlin extension). I just don't think that our existing tests will shed a lot of light on what normal users will need.

(Again, this might be what you have in mind; I wasn't sure how to read "ported" or perhaps how to interpret which "core set of unit tests" we would be talking about.)

[kevinb9n]

Yes, scratch all implication of where the tests come from; the point was just that a small set of tests covering different API interactions should exist in both languages.