Jest crashing on every decorator
NestJS decorators threw before any test ran until reflect-metadata was polyfilled explicitly in the Jest setup.
Two copies drifted
One idea kept by hand in two places — schema and migration, dev and prod, app and app.
Setting up the first real test run, the decorators that make NestJS work blew up before any test logic ran. The setup needed reflect-metadata polyfilled explicitly. Not interesting in itself, but it's the kind of thing that blocks everything behind it — nothing at all could be tested until it was fixed.