Baked test methods are marked incomplete.

Previously empty (and "passing") test methods now include PHPunit's `markTestIncomplete()` to better reflect the truth of the resulting file: The test methods are stubbed out, but are not yet complete and passing.

It is much easier when _running_ tests to locate incomplete test methods.

Fixes 2437.
Merge pull request #2440 from beporter/feature/bake-test-marktestincomplete

Baked test methods are marked incomplete.

Fixes #2437