This test harness is meant to make sure the upstream clang-tidy passes we use still work as documented. It only matters when we upgrade clang, and even in that condition it is very unlikely to catch anything. Indeed existing autotests are very simple and are not comparable to upstream tests in terms of coverage. Those tests also consume resources and add an extra step when adding support for a new pass. Instead, we setup a task in Bug 2065029 that runs all clang static analysis on the whole tree and checks we don't regress. Differential Revision: https://phabricator.services.mozilla.com/D320205