Why is high code coverage not the same as good tests?
PICTURE THIS: DATA SPLIT
Fit on train, tune on val, report on test once.
Simple meaning
Coverage only shows which lines ran, not whether assertions would catch a bug.
WHY — Testing instead of guessing?
Why interviewers care about Testing:
on Testing.
the situation, the default choice, and one exception - that reads as experience.
Name the idea, why it exists, then one short example.
End with when you use it and one common pitfall.
STEPS — What happens step by step?
Before you speak the answer, walk the interviewer through these steps:
- 1Coverage only shows which
lines ran, not whether assertions would catch a bug.
- 2You can cover a
function with weak expects and still ship defects.
- 3Prefer tests for auth,
money, and data integrity over chasing 100 percent.
- 4Give an example
One tiny concrete case you can say aloud.
- 5Common mistake
What juniors usually get wrong.
- 6Close
When you pick this over the alternative.
EXAMPLE — See it in action
Here's a short line you can speak, broken into clear beats:
Note: Adapt this scaffold to your own project — keep it under 60–90 seconds.
Key takeaway
Coverage only shows which lines ran, not whether assertions would catch a bug. You can cover a function with weak expects and still ship defects.