Web and Mobile API Testing: A Detailed guide


Today, most applications are built using APIs. We have seen the rise of microservices and serverless computing, with each service being a small component that can be deployed independently and scaled as needed. This has also led to more integration points between applications, which brings us back to API testing.

API testing is a vital part of the software development process. It’s a black box testing technique that checks how two applications communicate with each other, ensuring that they work as expected.

It can be used to test backends of mobile apps (for example, Facebook Messenger) or any other kind of application that has an API interface exposed to external entities.

The aim of API testing is to make sure that the application works as expected. It can be used to test backends of mobile apps (for example, Facebook Messenger) or any other kind of application that has an API interface exposed to external entities.


Web API Testing, Mobile API Testing

What is an API?

API stands for Application Programming Interface, which is a set of routines, protocols, and tools for building software applications. APIs are used to integrate software components, allowing two computer programs to communicate with each other by sending data in a standard format. There are two types of APIs: web APIs and mobile APIs.

APIs are used to share data between different systems or applications (e.g., sharing information about users). They can also be used to build mobile apps that interact with remote servers or services over the internet via JSON requests/responses (JavaScript Object Notation).

What is API Testing?

API testing is crucial to ensure the quality of your web and mobile apps. It can be done by developers, QA engineers, and business analysts. It’s not just about testing the API endpoint and response, but also testing the backend of your mobile app or web app.

For example, if you want to build an app that lets users find nearby restaurants on their mobile devices and order food from them through the app itself, it might make sense for your app’s backend server codebase (the part where all the logic happens) to have an API call into Yelp’s database in order for this feature work properly – otherwise, it would just be sending all its queries directly over cellular networks which would be very slow!

Here’s another real-life API testing example. Let’s say you are testing the backend API of a mobile app that allows users to create and manage to-do lists. Here are some test cases you might want to consider:

  • Test API authentication: Ensure that the API requires authentication to access it. Verify that a valid user can log in and receive an authentication token, while an invalid user is denied access.
  • Test API response codes: Check that the API returns the expected HTTP status codes for various requests, such as success (200), bad request (400), unauthorized (401), and not found (404).
  • Test CRUD operations: Verify that users can create, read, update, and delete to-do lists and their associated tasks. For example, create a new to-do list, verify that it appears in the list of user’s to-do lists, update an existing task, and confirm that the changes are reflected in the backend.
  • Test input validation: Ensure that the API properly handles invalid input, such as empty fields or incorrect data types. Verify that the API returns appropriate error messages for these scenarios.
  • Test API security: Verify that the API is secure and protected from common security threats such as SQL injection and cross-site scripting (XSS) attacks.
  • Test API performance: Test the API’s response times and verify that it can handle a high volume of requests without performance degradation.

By testing these and other relevant scenarios, you can ensure that the API backend of the mobile app functions as expected and provides a seamless user experience.

Why Testing APIs?

API testing is important to ensure the quality of your web and mobile apps. API testing can be done by developers, QA engineers and business analysts.

API testing is not just about testing the API endpoint and response; it is also about testing the backend of your mobile app.

You can also perform API testing on a mobile device or emulator. You can use your own device to test the app, or you can use a cloud-based tool such as Google Cloud Test Lab.

API testing is also an important part of mobile app development. When you are building a mobile app, you need to make sure that the API endpoint works well with your backend. 

How to test APIs?

There are many ways to test APIs, including using tools like Postman and curl command line tools, or even an API testing framework like SoapUI. The most popular method for web and mobile API testing is to use a tool like JMeter, Katalon, Apigee, or Karate to automate API testing.

API testing with Postman:


  • Install Postman: First, you need to download and install Postman. Postman is a popular API testing tool that allows you to test APIs by sending HTTP requests to the server and receiving responses.
  • Create a new request: To create a new request in Postman, click on the “New” button on the top-left corner of the application. Then, select the type of request you want to send (e.g. GET, POST, PUT, DELETE) and enter the URL of the API endpoint you want to test.
  • Add request parameters: Depending on the API endpoint you’re testing, you may need to add request parameters to your request. These parameters can include headers, query parameters, and request body data. To add parameters in Postman, click on the “Params” or “Body” tabs, depending on the type of parameter you want to add.
  • Send the request: Once you’ve added all the necessary parameters to your request, click on the “Send” button to send the request to the server. Postman will display the response from the server, including the status code, response headers, and response body.
  • Validate the response: After you’ve received the response from the server, you need to validate it to ensure that it meets your expectations. You can use Postman’s built-in assertions to validate the response, such as checking the status code, response headers, and response body.
  • Create test suites: Once you’ve created a few requests and validated their responses, you can create test suites to automate your API testing. Test suites allow you to group related tests together and run them all at once. You can also set up assertions for each test to ensure that they pass or fail based on specific criteria.

Overall, Postman allows you to test APIs quickly and easily. It’s easy to get started with, and you can create more advanced tests and test suites as you become more familiar with the tool.


API testing with SoapUI:


SoapUI is another popular tool for API testing that provides a comprehensive set of features to help testers create and execute automated functional, regression, compliance, and load tests for REST and SOAP APIs. Some of the key features of SoapUI include:

  • Easy API Discovery: SoapUI allows users to easily discover APIs by importing WSDL, Swagger, or RAML definitions, making it easy to get started with testing.
  • Automated Testing: SoapUI allows testers to create automated tests using its intuitive drag-and-drop interface, without needing to write any code. It also supports scripting languages like Groovy and JavaScript for more advanced test scenarios.
  • Test Data Generation: SoapUI provides tools for generating test data and creating data-driven tests, allowing testers to cover a wide range of test scenarios.
  • Mock Services: SoapUI allows testers to create mock services that simulate the behavior of the actual API, allowing testing to proceed even when the actual API is not yet available.
  • Integration with CI/CD: SoapUI integrates with popular CI/CD tools like Jenkins, Bamboo, and TeamCity, allowing teams to include API testing as part of their automated testing pipeline.


Overall, SoapUI offers a wide range of features and customization options. With SoapUI, testers can easily create and execute automated tests for their REST and SOAP APIs, ensuring that their APIs are working as expected and meeting the requirements of their users.

API testing with the Katalon Platform


The Katalon Platform is a powerful test automation solution  that allows you to easily create and run tests for web and mobile applications, including APIs.

Some additional features of Katalon that can be useful for API testing include:

  • Data-driven testing: Katalon allows you to use data from external sources, such as CSV or Excel files, to drive your API tests. This can help you test your API with different inputs and scenarios.
  • Assertions: Katalon provides a range of built-in assertions that you can use to verify the responses from your API endpoint. This includes checking response codes, response headers, and response content.
  • Reports: Katalon generates detailed reports for each test case, including screenshots and logs. This can help you identify any issues or errors that occur during your API testing.
  • Seamlessly integrations: Katalon allows users to automate API testing without depending on third-party tools or configurations while leveraging all the benefits of the Katalon Platform.
  • Flexible Parametrization: with Katalon, users can parametrize any value within the API interface and use external data sources like excel, text files, databases, etc. to inject values into the API parameters. This technique enables users to use the same test case to test on multiple environments and streamline the testing cycle.

Overall, Katalon is a powerful tool for API testing that can help you ensure the quality and reliability of your web and mobile applications.

Web API Testing vs Mobile API Testing?

Web API testing is the process of testing the backend of a mobile app, while mobile API testing is the process of testing the actual app itself.

Web API testing is more complex than mobile API testing because it involves more components like databases and servers.

Mobile developers can start with web API testing and then move on to mobile API testing once they’re comfortable with their understanding of how data flows through their system.


Testing is important because it allows us to make sure that our apps are working properly and secure. It also helps us identify any bugs or issues before they become a problem for our users.

We hope that you have learned about the importance of testing your APIs and how it can help you ensure the quality of your web and mobile apps.

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