You're probably thinking of complaints that our CI was flakey at times (failing despite changes being ok), which is true (though it's been pretty stable lately). However, people sometimes equate that with bad test coverage, which is absolutely not the same thing. Easiest way to get a test to pass is to delete it.
From my perspective at least, the julia test suite is quite comprehensive (if something passes the test suite, I'm generally happy to put it on master and have people use it). We're also lucky that there is so much open source julia code available, which we can use as essentially one giant regression test. We used that heavily in the lead up to 1.0 to make sure that there weren't any surprise bugs waiting for people.