Drop CMake option SEPARATE_TESTS

[dalg24]

I am trying to cleanup the logic of the test registration in core/unit_tests and I am tempted to drop the if(SEPARATE_TESTS). I personally like the finer granularity (option set to ON).

Can you think of one reason one might want to have a single executable for the core unit tests?

cc: @crtrott @jjwilke

[jjwilke]

No opinion. I don't actually know the history of this.

[crtrott]

Oh I didn't know that someone added that. I personally like the have everything for a backend in one executable and use --gtest-filter for choosing individual tests.

[dalg24]

Oh I didn't know that someone added that. I personally like the have everything for a backend in one executable and use --gtest-filter for choosing individual tests.

Fine by me. Then I will drop the option and always do a single executable.

[crtrott]

We may have had some weird link issues on some early experimental compilers before (like OpenMPTarget, or ROCm) but I think we can handle that via the standalone unit test during experimental development phase. And if they can't link our unit tests for one backend, there is no way they can link a Trilinos executable anyway ...

[dhollman]

I added this option (sorry I missed this conversation!). I mostly added this because tests were taking forever to recompile (because of Kokkos' "include everything everywhere" philosopy) and the only tests I was expecting to change behavior were the tasking tests. The --gtest-filter option doesn't work for this purpose because you still have to recompile every test (for a given backend) even to just run one test. That's a real pain when working on Kokkos itself, and discourages our team from compiling and testing early and often.