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POSTMAN

Postman, APIs, and all the testing chaos—unfiltered

In this Postman API Testing Tutorial

Complete Postman API Testing Tutorial for Beginners

Alright, come closer. Let me tell you how I royally screwed up the first time I touched Postman. It was 2014. I copy-pasted some URL into the app, hit “Send,” and stared blankly at the 401 Unauthorized like it was a puzzle from Interstellar. No one told me what headers were. Or what a Bearer token was. Or why APIs feel like they’re playing hard to get.

So yeah—I wrote this guide for you. For the tester who’s just opening Postman and wondering: What the heck am I supposed to do with this? Or the dev who’s been pretending to understand APIs at standups.

Let’s break it all down—no jargon, no fluff, just real talk.

What is Postman & Why Should You Care?

It’s not just a REST client. Postman is like the Swiss Army knife for API testing—manual, automated, exploratory, scripted—you name it.

Here’s what it’s actually good for:

  • Hitting endpoints like a boss (GET, POST, PUT, DELETE…)

  • Checking if your dev’s new API is lying

  • Automating smoke tests for your microservices

  • Building collections so future-you doesn’t cry

Installing Postman

Wait—I almost forgot… it’s free. You’re welcome.

The Postman UI: What Button Does What

Here’s a quick map:

  • New – Create a request, collection, etc.

  • History – All your past fumbles and wins

  • Collections – Where your organized chaos lives

  • Request Builder – The main screen where you build/test calls

  • Params/Header/Body/Auth tabs – All the scary things, neatly separated

  • Tests tab – Where JS magic happens

Making Your First API Call

Steps:

  1. Open Postman

  2. Select method: GET

  3. Paste this: https://jsonplaceholder.typicode.com/posts/1

  4. Click Send

  5. 🎉 Boom. You just hit an API.

What to look for:

  • Status = 200 OK

  • Body = JSON response

  • Time = How fast the server danced for you

Want to try POST?

  1. Change method to POST

  2. URL: https://jsonplaceholder.typicode.com/posts

  3. Body > Raw > JSON:

				
					{
  "title": "hello",
  "body": "world",
  "userId": 1
}

  4. Hit Send

Common HTTP Methods Explained

  • GET – Fetch data (read-only)

  • POST – Create new data

  • PUT – Update entire object

  • PATCH – Partial update

  • DELETE – Nuke it from orbit

Use them wrong and your test will look right but be completely useless.

Headers, Params & Auth

  • Params – Added to URL (e.g. ?id=1)
  • Headers – Think of these as your test’s ID badge
  • Authorization – The bouncer at the API club
Example Header:
Content-Type: application/json
Authorization: Bearer <your_token>

If you don’t pass the right headers? You’ll get smacked with a 401 or 403 faster than you can say “debug.”

Collections: Save Yourself Some Sanity

Collections = folders of requests.

Why you need them:

  • Keep related requests together
  • Share with team
  • Run them in a batch (hell yes)

Create one, add requests, save it. Done.

Environments & Variables

Tired of copy-pasting base URLs or tokens?

Set up Environments like:

{{baseUrl}} = https://api.dev.example.com
{{authToken}} = abc123

Use them in your requests like:

{{baseUrl}}/users

Switch environments without rewriting everything = BIG win.

Test Scripts in Postman (With Example)

Want to automate validation right inside Postman?

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

You can validate headers, response body, schema, whatever your nerdy heart desires.

Collection Runner, Pre-Request Scripts & Monitors

Collection Runner:
  • Run an entire collection (great for regression tests)
  • Use test data files (CSV/JSON)
  • See pass/fail summary
Pre-request Scripts:
  • JS code that runs before request is sent
  • Use to set tokens, timestamps, etc.
Monitors:
  • Schedule your collection to run hourly/daily
  • Monitor uptime or API health (DevOps teams love this)

What Makes a Bad vs Great Postman Test

Bad:

  • Only checks if 200 OK returned
  • Doesn’t validate response body
  • Hardcoded tokens/URLs
  • Can’t be reused or shared

Great:

  • Validates data
  • Uses variables
  • Part of a collection
  • Clean, named, commented tests

🧪 Mini Case Study

Worked with a team building APIs for a fintech app. I set up Postman tests that:

  • Authenticated user via login API
  • Pulled user’s balance
  • Posted a transfer request
  • Checked transaction logs

Catch? Dev forgot to set Content-Type. My test caught it before prod. 💥

✅ Do’s & Don’ts

Do:
  • Use variables for URLs and tokens
  • Group requests in collections
  • Write assertions in test tab
  • Use environments wisely
  • Share collections with the team
Don’t:
  • Manually copy-paste headers each time
  • Assume 200 OK means success
  • Hardcode anything
  • Skip checking actual response data

FAQs

Yes—for most use cases. For full-scale automation, use Newman in CI.

Yup. It has native GraphQL support.

Use Authorization tab > OAuth2 and follow the flow. Save token to env

Depends. For manual/exploratory? Postman wins. For automation pipelines? Rest Assured.

Absolutely. Use the form-data option in the Body tab and select File type for the key you want to upload.

Click the Share button on your collection. You can invite team members or export it as a JSON file to send manually.

Local variables are tied to an environment. Global variables are available everywhere. Use local when possible to avoid conflicts.

Yes. Use the Collection Runner or test scripts to set variables from one request and use them in the next.

Use pre-request scripts in JavaScript to generate dynamic values and store them in variables.

Yup. Export your collections/environments as JSON files and include them in your repo. You can also use Postman’s integration with GitHub.

Use Mock Servers in Postman to simulate API responses based on your collection.

You’re likely only testing status codes or missing key validations. Always test actual response content, formats, and edge cases.

💬 Conclusion & Call to Action

You made it. That already puts you ahead of half the devs I know.

If you:

  • Learned something

  • Screamed at your screen

  • Found a better way to do it

👉 Drop it in the comments. Let’s swap war stories.
Comment below if you’ve ever rage-quit Postman. No judgment—just stories.

And if you’re still confused about something? Ask. No shame. We all start somewhere.

Please check our blogs.

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