Postman Writing Tests

Postman lets you write automated tests that check whether an API response is correct. After each request runs, these tests verify that the data, status code, and structure meet your expectations. You write tests in JavaScript using Postman's built-in pm object.

Why Automated Tests Matter

Imagine testing a login API manually every day. You would send the request, read the response, check the status code, and look for a token. Now imagine doing this for 50 endpoints. Automated tests do all of this in seconds and tell you exactly which check failed and why.

Without Tests:             With Tests:
  Send request               Send request
  Read response              Tests run automatically
  Check status code          ✅ Status is 200
  Check response body        ✅ Token exists in body
  Remember to check headers  ❌ Response time exceeded 500ms
  Note findings              Results logged and saved
  Repeat for every request

Where to Write Tests in Postman

Click the Scripts tab (previously called Tests tab) below the URL bar in any request. Choose the Post-response section. Code you write here runs automatically after each response arrives.

The pm Object

Postman provides a global pm object in all scripts. It gives you access to the request, the response, variables, and a testing interface.

Write Your First Test

Open a GET request to https://jsonplaceholder.typicode.com/users/1 and go to the Scripts → Post-response section. Write this test:

pm.test("Status code is 200", function () {
    pm.response.to.have.status(200);
});

Click Send. The Test Results tab appears in the response panel and shows a green checkmark next to "Status code is 200". A red cross appears if the test fails.

Common Tests You Will Write

Check Status Code

pm.test("Status is 200 OK", function () {
    pm.response.to.have.status(200);
});

Check a Field in the Response Body

pm.test("User name exists", function () {
    const data = pm.response.json();
    pm.expect(data.name).to.be.a("string");
});

Check a Specific Value

pm.test("User ID is 1", function () {
    const data = pm.response.json();
    pm.expect(data.id).to.equal(1);
});

Check Response Time

pm.test("Response time is under 500ms", function () {
    pm.expect(pm.response.responseTime).to.be.below(500);
});

Check a Response Header

pm.test("Content-Type is JSON", function () {
    pm.expect(pm.response.headers.get("Content-Type")).to.include("application/json");
});

Testing an Array Response

When an API returns a list of items, you can check the list is not empty and that items have the right shape:

pm.test("Posts list is not empty", function () {
    const posts = pm.response.json();
    pm.expect(posts).to.be.an("array");
    pm.expect(posts.length).to.be.above(0);
});

pm.test("Each post has a title", function () {
    const posts = pm.response.json();
    posts.forEach(function (post) {
        pm.expect(post).to.have.property("title");
    });
});

Use the Snippet Sidebar

Postman's Scripts panel has a Snippets section on the right side. It lists pre-written test templates. Click any snippet to insert it into your test area instantly. Common snippets include:

• Status code: code is 200
• Response body: JSON value check
• Response time is less than 200ms
• Response body: contains string

Snippets speed up writing and help you learn the correct syntax.

Test Results Panel

After sending a request with tests, click the Test Results tab in the response panel. Each test shows:

• A green PASS badge if the assertion succeeded
• A red FAIL badge with an error message if something went wrong

Test Diagram – Full Flow

  Request Sent
       │
       ▼
  Server Responds (200 OK, JSON body)
       │
       ▼
  Post-response script runs
       │
       ├── ✅ Status is 200        → PASS
       ├── ✅ Name is a string     → PASS
       └── ❌ ID equals 2         → FAIL (actual: 1)
       │
       ▼
  Test Results tab shows summary

Summary

Tests in Postman run automatically after each response using JavaScript in the Post-response section. The pm.test function defines a test and pm.expect checks values using Chai assertions. Tests verify status codes, response fields, values, headers, and response times. Use the Snippets panel to insert common test templates quickly and speed up your workflow.