Asking ChatGPT to Write the Tests Before the Function

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.