Pre-request Scripts in Postman

In Postman API testing, pre-scripts (also known as pre-request scripts) and post-scripts (test scripts) are used to add dynamic behavior to your requests. Here’s an explanation with real-life examples:

Pre-request Scripts

Pre-request scripts are snippets of code associated with a collection request that are executed before the request is sent. They can be used to:

• Set environment variables
• Generate timestamps or random data
• Authenticate requests
• Modify request headers

Pre-request Scripts in Postman: Simplified Explanation with E-commerce Example

Pre-request scripts in Postman are scripts executed before the main API request is sent. They can be used to set up necessary conditions or data for the request.

Example Scenario: E-commerce App

Let's say you are testing an e-commerce app's API, and you need to create a new product. The API requires a unique product ID, which you will generate dynamically in the pre-request script.

Step-by-Step Example

1. Generating a Unique Product ID

Pre-request Script:

// Pre-request Script

var uuid = require('uuid');

var productId = uuid.v4(); // Generates a unique identifier

pm.environment.set('product_id', productId);

In this script, we use the uuid library to generate a unique product ID and store it in an environment variable called product_id.

2. Creating a New Product Request

API Request:

POST https://api.ecommerce.com/products

Headers: Content-Type: application/json

Body (raw JSON):

{ "id":

"{{product_id}}", "name": "New Product", "price": 29.99, "category": "Electronics" }

In this request, we use the {{product_id}} variable, which was set in the pre-request script, to ensure each product created has a unique ID.

3. Validating the Response

Test Script:

Test scripts are executed after a request has been sent and a response has been received. They can be used to:

• Validate response status codes
• Validate response body content
• Set environment or global variables based on the response
• Log information to the console
• Real-life Example:

Suppose you are verifying that a user registration API returns a 201 status code and includes a user ID in the response.

Sending the Request:

POST https://api.example.com/register

Body: { "username": "john_doe", "password": "securepassword123" }

Test Script to Validate Response:

// Test Script

pm.test("Status code is 201", function () {

pm.response.to.have.status(201); });

pm.test("Response has product ID", function () {

var jsonData = pm.response.json();

pm.expect(jsonData).to.have.property('id'); });

In this script, we validate that the response status code is 201 (Created) and that the response body contains the product ID.

Summary

Pre-request Script: Generates a unique product ID before the API request is sent.

API Request: Uses the generated product ID to create a new product.

Test Script: Validates the response to ensure the product was created successfully.

This example demonstrates how pre-request scripts can be used to dynamically generate data needed for API requests in a simplified and practical e-commerce scenario.