Can someone explain the output from running Bitcoin Core unit tests on Mac OS please?
This is the output for all platforms at the moment, not just MacOS. To paraphrase from sipa on IRC:


The first summary is bitcoin's own summary: because of some hackery to run unit tests in parallel, it currently shows no tests (even though they are executed).
The second and third summary are the output from make check for the built-in dependencies, secp256k1 and univalue respectively.