How To Use Postman To Test Api Endpoints

Getting Started with Postman for API Testing

Postman is a powerful tool for interacting with APIs, offering a user-friendly interface for sending requests, inspecting responses, and managing API documentation. This guide will walk you through the basics of using Postman for testing API endpoints.

Installing Postman

Postman is available as a desktop application for Windows, macOS, and Linux, as well as a web-based version. You can download the desktop app from the official Postman website: https://www.postman.com/downloads/.
To use the web-based version, sign up for a free account: https://app.postman.com/signup/

Creating a New Request

Once you’ve installed and opened Postman, you can create a new request. Here’s how:

1. Select New: Click on the “New” button in the top left corner of the Postman window.
2. Choose Request: From the dropdown menu, choose “Request”.

Defining the Request Method and URL

After creating a new request, you’ll need to define the HTTP method and the endpoint URL.

1. Select Method: Use the dropdown menu to choose the appropriate HTTP method (e.g., GET, POST, PUT, DELETE).
2. Enter URL: In the address bar, enter the complete URL of the API endpoint you want to test.

Example:

For a GET request to the endpoint https://api.example.com/users:

• Method: GET
• URL: https://api.example.com/users

Sending a Basic Request

To send a request, simply click the “Send” button in the top right corner of the Postman window.

Inspecting the Response

After sending the request, Postman displays the response in the “Body” tab.

• Inspect the status code: This appears in the top-right corner of the “Body” tab; a 200 status code indicates success.
• Analyze the response data: Postman can display the response data in various formats like JSON, XML, plain text, etc.
• Verify the response content: Make sure the response data matches your expectations based on the API documentation.

Testing API Endpoints with Different Methods

Postman allows you to test various API endpoints with different request methods. Here are practical examples for commonly used methods:

Using GET for Data Retrieval

Let’s test the https://api.example.com/users endpoint to retrieve a list of users.

Steps:

1. Create a new request: Follow the instructions for creating a new request.
2. Set the method to GET: In the method dropdown, choose “GET”.
3. Enter the URL: In the address bar, enter https://api.example.com/users.
4. Send the request: Click the “Send” button.

Expected Response:

• Status Code: 200 (Success)
• Response Body (JSON):

[
  {
    "id": 1,
    "name": "John Doe",
    "email": "john.doe@example.com"
  },
  {
    "id": 2,
    "name": "Jane Doe",
    "email": "jane.doe@example.com"
  }
]

Using POST for Data Creation

Let’s test the https://api.example.com/users endpoint to create a new user.

Steps:

1. Create a new request: Follow the instructions for creating a new request.
2. Set the method to POST: In the method dropdown, choose “POST”.
3. Enter the URL: In the address bar, enter https://api.example.com/users.
4. Provide data in the Body: In the “Body” tab, select the “raw” option and choose JSON as the format. Enter the following JSON data.

{
  "name": "New User",
  "email": "newuser@example.com"
}

5. Send the request: Click the “Send” button.

Expected Response:

• Status Code: 201 (Created)
• Response Body (JSON):

{
  "id": 3,
  "name": "New User",
  "email": "newuser@example.com"
}

Using PUT for Data Update

Let’s test the https://api.example.com/users/1 endpoint to update the user with id 1.

Steps:

1. Create a new request: Follow the instructions for creating a new request.
2. Set the method to PUT: In the method dropdown, choose “PUT”.
3. Enter the URL: In the address bar, enter https://api.example.com/users/1.
4. Provide data in the Body: In the “Body” tab, select the “raw” option and choose JSON as the format. Enter the following JSON data.

{
  "name": "Updated User"
}

5. Send the request: Click the “Send” button.

Expected Response:

• Status Code: 200 (Success)
• Response Body (JSON):

{
  "id": 1,
  "name": "Updated User",
  "email": "john.doe@example.com"
}

Using DELETE for Data Removal

Let’s test the https://api.example.com/users/1 endpoint to delete the user with id 1.

Steps:

1. Create a new request: Follow the instructions for creating a new request.
2. Set the method to DELETE: In the method dropdown, choose “DELETE”.
3. Enter the URL: In the address bar, enter https://api.example.com/users/1.
4. Send the request: Click the “Send” button.

Expected Response:

• Status Code: 204 (No Content)
• Response Body: Empty

Adding Authorization

Many APIs require authorization to access resources. Postman provides several ways to add authorization:

• Basic Auth: Enter your username and password.
• Bearer Token: Provide an access token.
• API Key: Include an API key in the request headers.

Example (Bearer Token):

1. Click the Authorization tab in the request window.
2. Select Bearer Token.
3. Enter your access token in the Token field.

Using Environment Variables

Environment variables allow you to store and manage different sets of values for testing across various stages of development (e.g., development, testing, production). They’re useful for:

• Replacing hardcoded values: Avoid hardcoding URLs or other sensitive data.
• Organizing settings: Group related settings for different environments.

Example:

1. Create an environment: Click the Environments tab and then “Add”.
2. Define variables: Give meaningful names to the variables and provide their values. For example, you might have baseUrl, apiKey, etc.
3. Use variables in your requests: Enclose variable names in double curly braces (e.g., {{baseUrl}}/users).

Creating Collections

Postman collections allow you to group related requests, making it easier to organize and run a sequence of tests.

Example:

1. Create a new collection: Click the Collections tab and then “Create Collection”.
2. Add requests to the collection: Drag and drop individual requests into the collection or use the “Add Request” button to add them.
3. Run the collection: Click the “Run” button in the collection window to execute all requests in the collection.

Using Test Scripts

Postman allows you to write JavaScript code to run tests on your API responses. These tests help automate verification of expected results.

Example:

1. Add a test tab: Click the test tab within a request.
2. Add tests: Write JavaScript tests to validate response status codes, response data, and other aspects of the API response.

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

pm.test("Response data contains 'name'", function () {
  pm.expect(pm.response.json().name).to.be.a('string');
});

Postman’s benefits for API testing

• Simplified Testing Process: The intuitive interface simplifies the process of sending requests, validating responses, and managing tests.
• Collaborative Testing: Sharing collections and environments with team members allows for efficient collaboration and knowledge sharing.
• Automation: Postman’s test scripts and collections enable automated testing and continuous integration pipelines.
• API Documentation: Postman facilitates generating API documentation, including details of endpoints, request methods, parameters, and expected responses.

Postman is a powerful tool that can help you efficiently test your APIs, ensure their quality, and accelerate development cycles.