Lesson 982 of 1455
Asking ChatGPT to Write the Tests Before the Function
Generating tests with AI before the function makes the AI's actual code much easier to trust.
Builders · AI-Assisted Coding · ~4 min read
The big idea
If you ask ChatGPT 'write me a function that does X' you get code you have to trust. If you first ask 'write me 5 tests for a function that does X' and then 'now write the function to pass these tests' — you can run the tests and *see* it works. Same AI, way more trustworthy.
Some examples
- You ask Claude for tests for a 'parse a date string' function — the tests reveal you never decided about empty strings.
- ChatGPT writes tests for a leap-year checker that catch year 1900 (not a leap year, despite divisible by 4).
- Cursor writes tests for a username validator that include emoji — you decide your policy on the spot.
- Copilot tests a sort function with already-sorted, reverse-sorted, and one-element arrays — pro-grade coverage you'd skip alone.
Try it!
Pick a tiny function (max 10 lines) you need this week. Ask an AI for 5 tests first. Read them, fix any wrong ones, then ask for the function. Run the tests.
Key terms in this lesson
End-of-lesson quiz
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