I'd like support for a make target, available in every directory via rules.mk or similar inheritance, which automagically runs *all* the tests (C++, xpcshell, mochitest, etc). :biesi said `make check` used to do this, but it broke a while ago. If something is available already, https://developer.mozilla.org/en/Mozilla_automated_testing should probably be updated to say how to invoke it. Expected behavior: `make -C any/path/in/obj/dir tests` just works.

"make check" never used to do this. It used to run the check:: targets, which ran compiled C++ tests, as well as xpcshell tests. It never ran mochitest/reftest/etc. Those would be a little trickier to handle, since the Makefiles don't actually know about them, but we could probably sort something out.

Having explicit variable(s) to define test directories will help here.