PI unittests fail when no OpenCL RT is available

[smaslov-intel]

Great thanks for doing this! The PI tests will be build always, but when/how are they run?

@smaslov-intel This now works as in Clang and the other LLVM projects:

• When SYCL testing is enabled with the CMake flag SYCL_INCLUDE_TESTS then the unittests are added as a dependency to the LIT tests (see CMake variable SYCL_TEST_DEPS).
• This in itself ensures that the unittests are build when the other LIT tests are build, e.g., by running the build for the check-sycl target.
• The LIT tests folder now has a Unit sub-folder which contains LIT config files that are gtest aware and are pointed to the unittests build directory to discover all included test executables to run.

Originally posted by @bjoernknafla in #585 (comment)

[smaslov-intel]

@bjoernknafla, it appears that these tests cannot pass on a system that does not have OpenCL. We should either skip these tests somehow, or make them to report "pass" in such circumstances (and maybe emit a warning for a careful tester).

[bjoernknafla]

How urgent is this problem? Is this breaking automatic testing?

Introducing PI backend discovery to the PI unittests would automatically deal with not finding any platforms and devices. My guess is that it will look like the unittests passed even though not a single one ran.

I dislike how this can hide problems though, e.g., if the lookup mechanism for PI plugins fails the testing would still look ok instead of failing to warn about the problem.

I need to think a bit more about this. Any feedback and thoughts are highly welcome how to ensure solid testing.

[smaslov-intel]

Yes, this is breaking the testing that is legally performed on machines not having the full run-time setup.

if the lookup mechanism for PI plugins fails the testing would still look ok instead of failing to warn about the problem.

I think we should just separately test for PI discovery to work correctly, which is TBD.

[bjoernknafla]

See PR for a fix: #748

[AlexeySachkov]

@smaslov-intel, looks like fix was provided, can we close this issue?

[smaslov-intel]

Yes