We seem to be talking at cross-purposes here. I agree that tests enforce backwards compatibility (or compatibility in general) but they also enforce a particul

We seem to be talking at cross-purposes here. I agree that tests enforce backwards compatibility (or compatibility in general) but they also enforce a particular design. Fundamentally redesigning something generally involves breaking the testa and the API. To put it another way, if you never break your tests you can only ever fix bugs or add more code -- you can never remove code or redesign.