Add unit tests for converting SDF to USD

[adlarkin]

Signed-off-by: Ashton Larkin [email protected]

🎉 New feature

Summary

Adding unit tests for converting things like lights and models from SDF to USD.

Test it

You can build SDF and run the UNIT_sdf_usd_TEST executable:

mkdir build
cd build
cmake ..
make -j 10
cd build/src
./UNIT_sdf_usd_TEST

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[koonpeng]

usd has a known bug PixarAnimationStudios/OpenUSD#86 which causes it to exit the process cleanly if there is a fatal error. This can cause ci to stop early and report success if the program ever "crashes".

I can think of some workarounds

1. fix upstream
2. make all tests death tests, this is an ugly workaround which forks the process for every tests, the googletest docs mentions issues with forks which need to be worked around as well http://google.github.io/googletest/advanced.html#death-tests-and-threads.
3. make a custom test runner which either captures and check stdout of the tests, or have each test write some artifacts and have the runner check them at the end.

[adlarkin]

I am going to close this PR since the testing done here has been moved to #818, but I realize that we probably still need to address #796 (review) at some point. I have made a separate issue for this so that it can be discussed and worked on there: https://github.com/ignitionrobotics/sdformat/issues/826