I just had the same problem and solved it by adding the following to my server.js
const cors = require('cors')
app.use(cors())
Opening the dev-console (F12) on the fcc testing site revealed there was a cors issue which made it impossible for the testrunner to access the package.json on my machine.
I don’t know why this is necessary here since other projects (like the helmet.js project before this one) seems to relax the cors settings via fcctesting.js just fine.
Side note: configuring cors like this has negative security implications but if you are only running the API locally, it will hopefully be okay.