As we refactor both the design and code, we should write tests for every function as quickly as possible to establish a rapid feedback loop for detecting any issues.
The current DevOps philosophy toward tech productivity is explicit about these sorts of goals: get feedback as early as possible, test as early as possible, and think about security and production environments as early as possible. This is all bundled into the idea of “shifting left” in the developer workflow; the earlier we find a problem, the cheaper it is to fix it.
As we refactor both the design and code, we should write tests for every function as quickly as possible to establish a rapid feedback loop for detecting any issues.