CMake fail target build if tests fail

I'm trying to attach unit tests to a specific target. I would like the tests to run as part of the target build, and if the tests fail, then the target should be considered 'unbuilt' or invalid such that the next time make is run the build will fail.

At the moment, I tried running the tests as a post-build custom command, but the tests only fail the first time they're run and subsequent tries will succeed (because the target is built).

How can I achieve this end?