Step 15: 100% code coverage for backend end to end tests

Since we now have thorough code coverage reports, let’s get those coverage numbers to 100%. This PR does it for the backend.

Oh god, I just noticed the branches are not fully covered! It’s all green, so I thought it’s done, but now as I’m publishing the screenshot I’m noticing some branches are still not covered… oh well, next time.

Cheers,
Andrew