JavadocTester now has a build-in link checker, that is enabled by default, but although it detects missing file, it does not (currently) treat them as serious errors causing a test to file. It should.

Fixing JavadocTester is a simple one-line fix, but doing sp exposes a number of test failures, where the link checker finds missing files. Most are benign and are easily fixed within the test; but one is a minor issue in javadoc itself, generating a reference to the default stylesheet when an overriding stylesheet has been provided. Even that fault is mostly benign, other than tripping up a link checker, because in that instance the (missing) stylesheet is not actually used.