How to Write Tests for AI-Generated Code

What Is a Test?

A test is a tiny program you write that checks whether another part of your code is doing its job correctly. Think of it like a spell-checker, but for code — it reads your code's output and tells you if something went wrong.

When an AI writes your code, you might assume it's perfect. It's not. AIs can leave out details, misunderstand what you wanted, or mix up how two parts of your program talk to each other. Tests catch those mistakes before your users do.

A test is really just three steps:

1. Set up — give your code something to work with
2. Run — let the code do its thing
3. Check — see if the result matches what you expected

AI Code Can Look Right But Be Wrong

When you write code yourself, you know what you were thinking. When an AI writes code, you only see the result. The code might look clean and complete but still have bugs hiding inside it — things that work in normal cases but break when a user types something weird, or leaves a field empty, or uses a special character.

Tests protect you from those surprises. Every time you make a change, you run your tests. If something breaks, the test tells you right away — not three days later when a customer reports a problem.

A Simple Test Flow

Here's how to test AI-generated code in three easy steps:

Step 1 — Know what the code should do. Before you test anything, write down what the code is supposed to produce when given a specific input.

Step 2 — Write a test that checks that. A test sends in a known input, runs the code, and confirms the output matches your expectation.

Step 3 — Run the test every time you change the code. This is the biggest habit to build. Each time you ask the AI to update your code, run your tests. If they all pass, you're good. If one fails, you know exactly what to fix.

A Test for a Calculator Function

Let's say the AI wrote a function that multiplies two numbers together. You want to test it. Here's what that looks like in plain English, then in code:

The multiply function should return 20 when given 4 and 5.
It should return 0 when one of the numbers is 0.

Now here it is written as an actual test:

// Test: multiply(4, 5) should equal 20
const result = multiply(4, 5);
if (result === 20) {
  console.log("✅ Test 1 passed");
} else {
  console.log("❌ Test 1 failed: got", result);
}

// Test: multiply(4, 0) should equal 0
const result2 = multiply(4, 0);
if (result2 === 0) {
  console.log("✅ Test 2 passed");
} else {
  console.log("❌ Test 2 failed: got", result2);
}

If both print "✅", your AI-generated function works. If either shows "❌", you have a bug to fix.

Knowledge Check

Test what you learned with this quick quiz.