Writing tests with AI help

What a test is

An automated test is a small program that checks your main program. Example: "When I add a task titled 'Buy milk', the open-task count increases by one." If someone changes the code later and breaks that behaviour, the test fails and you hear about it before a customer does.

Tests are not about mistrusting Cursor. They are about mistrusting complexity. Every new feature can accidentally break an old one. Tests act as guardrails.

How to ask Cursor for tests

Open Composer with your project loaded and try:

Add automated tests for the task tracker. Cover adding a task, marking a task complete, and deleting a task. Use the same test runner the project already uses. If no runner exists yet, propose Vitest or Jest with a short reason, wire up npm test, and keep the config minimal.

Let Cursor add or update files. Read the summary. If it wants to install packages, make sure you recognise the names.

Run tests inside Cursor

You already met the integrated terminal in Lesson 1. Use it again so you never leave Cursor.

1. Open the terminal panel (Ctrl + ` on Mac and Windows in most setups).
2. Make sure the prompt path matches your project folder (the same folder you opened with File > Open Folder).
3. Type npm test and press Enter.

Reading the output

• Green or the word PASS means the checks succeeded.
• Red or FAIL means at least one check broke. Scroll to the first stack trace; the error message usually names the test and the line.

If npm test says "missing script," open package.json and look for a scripts block. Cursor may have added "test": "vitest run" or similar. Run the exact command Cursor documented in the README or in Composer's summary.

If nothing runs yet

Ask Cursor: "Wire up npm test for this repo and show me the one command I should run after every change." Accept the smallest setup that works.

Good habits

• Run tests before you declare a feature "done."
• When a test fails right after a change, fix the code or fix the test. Ask Cursor which is wrong if you are unsure.
• Keep tests close to the behaviour they describe. If a test name confuses you, rename it in plain English.

What is next

You now have a local app you can change with words, read with guidance, iterate safely, and check with tests. The last lesson explains what deployment means and how Course 3 will pick up from here.

Next: You have a working local app