Creating more than one entry is not a “scaling issue”.
Unit tests are good, yes. Monitoring is also good. But just taking 30 seconds to do some manual testing will catch a LOT of unexpected behavior.
1. Get it working: write the code for the desired behavior, not worrying about making it beautiful, testable, whatever.
2. Get it working well: manually testing and finding edge cases, refactoring to get it testable and writing tests to solidify behavior.
3. Get it working fast: optimizing it to be as fast as I need it to be (can sometimes skip this step). No tests should change here, but only new tests.