When I created a new JS module, contrary to what it says here, I didn't need to add it to dependencies. In fact, doing that broke the testing with the error:
Error: Unknown dependency: ext.wikispeech.highlighter
where the new module is ext.wikispeech.highlighter.js.
It may well be that I've done something, somewhere that I should've done differently, but if not, the documentation should be updated.
The patch where this happened: I097b969ce00274b5f8d16d98c9d7ffd8c12f4fe1.