Postman Setup & API Testing for Your NestJS Blog (Beginner‑Friendly Guide)

1) Install Postman

1. Go to postman.com/downloads.

2. Download the installer for your OS (Windows/macOS/Linux).

3. Install and open Postman. If you’re prompted to sign in, you can choose “Use the lightweight API client” to skip account setup.

Tip: Keep Postman updated—it ships frequent improvements to the client and testing features.

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2) Start your NestJS app (local)

In your project folder:

npm run start:dev

By default, NestJS serves on http://localhost:3000 (unless you changed the port in main.ts).

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3) Create a Postman Environment

Environments let you avoid hard‑coding URLs/tokens.

Create a new environment named “Local (Nest Blog)” with variables:

• base_url → http://localhost:3000

• token → leave empty for now (we’ll set it after login)

You’ll reference variables like this: {{base_url}} and {{token}}.

Switch the active environment (top‑right environment selector in Postman).

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4) Create a Collection for your API

Click Collections → New Collection and name it “Blog API (Local)”. Inside it, create folders:

• Auth (login, refresh)

• Users

• Posts

• Tags (later)

We’ll add requests to these folders as we build features.

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5) Your first request (GET /)

In the Blog API (Local) collection, add a request:

• Method: GET

• URL: {{base_url}}/

• Click Send → you should see the default Hello World JSON/string from your Nest app.

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6) Working with routes: params & query

A. List posts with pagination

• Method: GET

• URL: {{base_url}}/posts?limit=10&offset=0

• Save it as Posts → List posts.

B. Posts by author (path param)

• Method: GET

• URL: {{base_url}}/posts/author/:authorId
  In Postman, click Params → Path Variables and set authorId to 42. Save as Posts → Posts by author.

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7) Sending JSON bodies (create & update)

Always set the header Content-Type: application/json when sending JSON.

A. Create a post

• Method: POST

• URL: {{base_url}}/posts

• Headers: Content-Type: application/json, Authorization: Bearer {{token}} (optional until auth is added)

• Body → raw → JSON

{
  "title": "My first NestJS post",
  "description": "Hello, world!",
  "authorId": 42
}

Save as Posts → Create post.

B. Replace a post (PUT)

• Method: PUT

• URL: {{base_url}}/posts/:id (set id path variable)

• Body (full resource): send the complete post object.

C. Partially update a post (PATCH)

• Method: PATCH

• URL: {{base_url}}/posts/:id

• Body (partial)

{
  "title": "Updated title only"
}

D. Delete a post

• Method: DELETE

• URL: {{base_url}}/posts/:id

PUT vs PATCH: PUT replaces the entire resource; PATCH updates selected fields.

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8) Headers & Authorization (Bearer JWT)

As we add auth later, most endpoints will require a token. In requests that need auth, include:

Authorization: Bearer {{token}}

You can set this in the request’s Headers or in the Authorization tab (Type: Bearer Token → {{token}}).

Auto‑inject the token for the whole collection

In the collection Authorization tab, set Type = Bearer Token and Value = {{token}}. Child requests inherit this, so you don’t have to repeat it.

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9) Save the token automatically after login

When you implement POST /auth/login (later), have it return a JSON like:

{ "access_token": "<jwt>" }

In the Tests tab of your Auth → Login request, add:

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

const data = pm.response.json();
if (data && data.access_token) {
  pm.environment.set('token', data.access_token);
}

Now, once you log in, Postman saves {{token}} to the environment automatically.

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10) Add lightweight tests to any request

Open the Tests tab and paste checks like:

pm.test('response is JSON', function () {
  pm.response.to.be.json;
});

pm.test('request succeeded', function () {
  pm.expect(pm.response.code).to.be.oneOf([200, 201]);
});

pm.test('responded quickly', function () {
  pm.expect(pm.response.responseTime).to