The existing Load All Maps in Game test should work as-is. What kind of difficulties are you having with it?
Also, keep in mind that all tests marked with ATF_SmokeTest are run during every startup in non-Shipping builds, so you’ll want to avoid marking any tests that may take more than a few seconds with that flag (IIRC, ATF_SmokeTests will automatically fail if they take longer than 2 sec., but I’d have to double-check that).