Use Tests to Unlock Design Changes
Retrieval Prompts
- Why are dirty tests eventually a design liability?
- What does it mean for a test to carry one concept?
- How do tests make refactoring possible?
- Why is duplication in tests sometimes acceptable and sometimes not?
Compare and Distinguish
Explain the difference between:
- testing behavior vs testing implementation details
- fast feedback vs broad but slow confidence
- a descriptive test name vs a cryptic one
- test setup noise vs essential scenario setup
Common Mistake Check
If changing a private helper breaks many tests, the suite may be over-coupled to structure instead of behavior.
If your tests require huge setup for tiny cases, design boundaries may be wrong.
If the tests are too messy to trust, they will not protect a refactor for long.
Mini Application
Choose one function, method, or small class and do all of the following:
- write or improve three tests that each express one behavior
- refactor the production code in at least two steps
- confirm the tests still pass after each step
- record one design improvement the tests made safe
Evidence Check
You are done only when:
- the tests read clearly enough for another learner to understand the behavior
- at least one test name expresses a rule rather than just an input/output pair
- the refactor changed structure while preserving behavior