Write tests

[moacode]

We should write a combination of front end and back end tests to ensure the logic doesn't break on subsequent updates.

There's a lot of reasonably complex logic and states the front/back end can be in which should have tests written against.

Most important areas would be:

• Front end form step states
• Back end variant generation permutations
• Configurations GET/POST API endpoints

[moacode]

Estimate: At least a day to get basic coverage.