If the SignatureTest.isAPICheckMode method returns true, the sigtest doesn't report about added API members. This differs from how it worked in 2.2 b03. See the changes made in the SignatureTest.trackMember method near the line starting:
    "if (!isSupersettingEnabled && !isAPICheckMode() ..."

Since the JCK compiler signature test works in the APICheckMode, this makes the test less strict.

This may be by design, but then the JCK compiler signature test needs a way to override this.
The JCK has a mini test suite to self-verify the JCK compiler sigtest. It's located in the <jck7-master-workspace>/libs/general/unittests/compilersigtest . There is a readme file that describing how to use. This test suite fails due to this issue.