Skip to content
Postman API Testing Tips

How To Do Web Service Test Using Postman

API Testing Blog

Introduction to Web Service Testing with Postman

Postman is a popular tool for testing web services (APIs). It offers a user-friendly interface and several advanced features that make API testing efficient and comprehensive. This guide will walk you through the process of testing web services using Postman, covering various aspects of API testing.

Setting up Postman for Web Service Testing

  1. Install Postman: Download and install Postman from the official website (https://www.postman.com/). Postman is available as a desktop app and a web-based platform.

  2. Create a New Workspace: Workspaces in Postman help organize your requests, collections, and environments. Create a new workspace to manage your API testing projects.

  3. Import API Definition (Optional): If your API has a definition file (e.g., OpenAPI/Swagger), you can import it into Postman to generate requests automatically.

Building Your First Request

  1. Create a New Request: Click on the “New” button in Postman’s interface and select “Request”.

  2. Specify Request Details:

    • Method: Choose the HTTP method (e.g., GET, POST, PUT, DELETE) that your API endpoint requires.
    • URL: Enter the complete URL of the API endpoint you want to test.
    • Headers: Add any necessary headers, such as authorization tokens or content types.
    • Body: Define the request body if the API requires it (e.g., JSON, XML).

Example: Getting Data with a GET Request

Imagine you have a weather API with the endpoint https://api.example.com/weather/current?city=London. You can use a GET request to fetch the current weather data in London.

// Request Method: GET
// URL: https://api.example.com/weather/current?city=London
  1. Sending the Request: Click the “Send” button to execute the request.

Examining the Response

After sending the request, Postman displays the response in different tabs:

  • Body: Contains the response data in the expected format (e.g., JSON, XML).
  • Headers: Shows the response headers, including status codes and other information.
  • Cookies: Lists any cookies sent with the response (if applicable).
  • Test Results: Displays results from any tests you have added to the request.

Using Test Scripts to Validate Responses

Postman’s scripting capabilities allow you to automate response validation and enhance your testing flow.

  1. Add a Test Script: Click the “Tests” tab and write your test script using JavaScript.

  2. Sample Test Assertions:

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

    pm.test("Response has a valid JSON body", function () {
        pm.expect(pm.response.json()).to.be.an('object');
    });
    

    pm.test("City name is London", function () {
        var jsonData = pm.response.json();
        pm.expect(jsonData.city).to.equal('London');
    });

Parameterization for Efficient Testing

Parameterization allows you to reuse requests with different input values.

  1. Create Variables: Go to the “Variables” tab and define variables for your request parameters.

  2. Use Variables in Requests: Replace hardcoded values in your request with variables using double curly braces {{variable_name}}.

Example: Testing Weather API with Different Cities

// Variable: city
// Value: London


// Request URL: https://api.example.com/weather/current?city={{city}}

You can change the value of the “city” variable to test the API with different locations.

Utilizing Collections and Environments

Collections organize your API requests and related tests. Environments store shared settings, such as API keys, base URLs, and environment-specific variables.

  1. Create a Collection: In Postman, click the “Collections” tab and create a new collection.

  2. Add Requests to the Collection: Drag and drop requests into your collection.

  3. Create and Manage Environments: Create an environment to manage settings for your API tests.

Example: Testing a Movie API

You can create a collection named “Movie API” and include requests for various operations like searching for movies, retrieving details for a specific movie, and adding movies to a user’s watchlist. You can create separate environments for development and production instances of the API with different API keys and base URLs.

Testing Different Scenarios and Error Handling

  1. Test Edge Cases: Design requests to check API behavior with edge cases, such as invalid inputs, empty parameters, or large data sets.

  2. Handle Error Responses: Test for potential error responses (e.g., 400 Bad Request, 404 Not Found) and validate the error messages returned by the API.

Example: Testing Invalid Input for Movie Search API

Send requests with incorrect parameters like invalid movie titles or empty search queries to check how the API handles those scenarios.

Advanced Features for Efficient Testing

Postman offers advanced features to enhance your testing process:

  • Data-Driven Testing: Use data files to execute the same request with different values, improving test coverage.
  • Mocking: Simulate an API server for testing purposes without relying on the actual backend.
  • Chaining Requests: Execute multiple requests sequentially, simulating real-world workflows.
  • Assertions and Validation: Utilize comprehensive assertions and validation methods to check responses against expected values.

Conclusion

Postman empowers testers to effectively test web services, ensuring API quality and reliability. By following this comprehensive guide and exploring the available features, you can enhance your API testing capabilities and deliver robust applications. Remember to prioritize thorough testing, consider edge cases, and leverage the power of automation to streamline your workflow.

API Testing Blog