I ran "make check" and found only one test that the above diff breaks:
ert-test-test-result-expected-p.

I can't seem to figure out why it doesn't work. The test fails because
of these two:

(let ((test (make-ert-test :body (lambda () (ert-fail "failed")))))
  (should-not (ert-test-result-expected-p test (ert-run-test test))))
(let ((test (make-ert-test :body (lambda () (ert-fail "failed"))
                           :expected-result-type ':failed)))
  (should (ert-test-result-expected-p test (ert-run-test test))))

I tried to re-throw the ert-test-failed signal and still the above two
forms raise error an error.