Isn't this taking TDD to literally? Verifying that a new test is indeed broken doesn't deserve a separate commit. The presence of that test in the codebase with all tests passing is enough. If your devs are writing new tests that are already passing your team needs a better lead, not more build controls.
In normal development flow sure. But if the bug made it already to master I'd prefer the separate commit so it can be easily verified that the problem is gone.
