Testing Database Migrations

Manual testing before a release of Bearly Fit drives me nuts. Not because I want to do it, but because I mostly have to.

Unlike a lot of apps, the database lives entirely on your device. There's no external server or anything to sync to. So every time I want to:

• add a new table
• new index
• update a column etc

I have to do those migrations on device and that comes with a lot risk. What if you're 3 versions behind? What if you don't have a backup? What if the migration fails?

Also because of O/S quirks I can't just test this in a sandbox, I need to run my tests on physical devices / simulators (so no Jest + SQL Library).

The first time I did this - I installed the previous release and then installed the new release on top, I tested the entire start to finish over and over again.

The second time - I created a mechanism to build a seeded V1 and V2 database and then from a custom debug menu deep inside the app I added a button to replace the database from the devices filesystem with a known copy and known values, then restart the app and go through the migration process.

This time, I decided to do something a little different. I modified metro so it copies the database + config for previous version to the bundle and then from a React Native debug menu I added 3 options:

• Restore a previous config + database
• Restore from a previous backup (v1/v2/v3)
• Verify a backup

So now I can do 95% of testing very quickly without faffing about with reinstalls and the last 5% is mostly just belts and braces.

Eventually I want this to be a full E2E process, I had started building something like that, but it relies on a lot of hooks to give me confidence.

Thanks for reading! Going to do some more work on Bearly Fans now :)