How to Write Test Cases for API Testing: With Template

Today, all applications run on API. It connects one microservice to another, clients with servers, and runs the most basic yet essential application services. Clearly, a well-oiled API is imperative to ensure the smooth functioning of every system.

If API breaks down, the complete user experience and application are put at risk. And only proper API testing can secure the system from such downtime possibilities. We bring you this blog to talk about API testing, its components, and sample test cases for API testing. A sample API test case template is also provided to guide you through the complete testing process. Further, the idea is to help you realize why automation might be the right option when it comes to testing APIs.

But let’s get a brief about API testing first.

What is API Testing?

API testing is a type of software testing that undertakes the verification of application programming interfaces (APIs). The process involves checking APIs as individual components of the software and as integrated pieces that fulfill the required functionality in the application.

Other types of testing, such as Integration testing, Security testing, Reliability testing, Performance testing, and Functional testing come under API testing as well. As APIs run the most critical sections of every application, every different stage of testing includes API testing as a segment. It might include writing test cases for API testing to run them manually or automatically to verify the performance, functionality, integration, and security of the software.

Different APIs might require distinct test cases, input/output, and approaches for testing. For instance, REST APIs and SOAP APIs are two different types of APIs, and performing REST API testing might differ from executing SOAP API testing. But for now, we will discuss generic API test cases you can go through before making them highly specific.

Generic Test Cases for API Testing

While API test cases will differ based on your requirement and application functionality, there are a few general steps that you will probably find in every test case for API testing. Here is a series of generic test cases for you to understand better.

• Validate the API keys for minimum and maximum range/length
• Verify that these keys are answering the call requests if you are using JSON or XML APIs in your application
• Create a separate test case to validate XML and JSON Schema
• Verify the Parse response to parse out portions of the response data returned from the server
• Check the JSON Schema validation, the Field Type, and the Mandatory Fields
• Validate the Response headers and Negative Testcases response
• Identify and verify the handling of API error codes
• Verify the HTTP response and its code status
• Validate Response payload to determine their format and readability factor
• Test request chaining to identify the working of multiple APIs together
• Verify APIs with input parameters.
• Validate end-to-end CRUD (create, read, update, and delete) flow for application API
• Check database integrity test cases
• Verify file upload test cases

Sample API Testing Test Case template

Applications and websites use multiple API calls at every stage. One of the prime examples of an API call is performing the login functionality using third-party services, such as Google, Yahoo!, or Facebook. Whenever you choose to sign into an application or a website using your Google details rather than within the app option, you trigger an API request. This implies the online platform has an existing agreement with Google to access the information already supplied and available to them. Such API calls require proper testing and validation before being released to users.

We are taking the same example to write a sample test case for API testing for testing purposes, which is going to test the APIs in the backend.

Sl.No	Test Case Title	Priority	Severity	Steps	Expected Result	Actual Result	Status
1	Checking Google login functionality using valid users	High	High	1. Navigate to the application/website login page 2. Click on the Google icon present on that page for login 3. A prompt will appear. Select ‘Proceed’ or ‘Confirm’ the Google username for signing in 4. The application should allow the process and take you to the dashboard/homepage	Log in process successful	Fill based on observation	Pass/Fail
2	Checking Google login functionality using invalid users	High	High	1. Navigate to the application/website login page 2. Click on the Google icon present on that page for login 3. A prompt will appear. Select ‘Add a New Account’ to add another Google account to sign in 4. Add a Google account with the existing username but wrong password 5. A prompt will appear. Select ‘Proceed’ or ‘Confirm’ the Google username for signing in	The application should not allow you to process the request and must ask you to sign up using the same Google account before logging in	Fill based on observation	Pass/Fail
3	Checking Google login functionality for new users	High	High	1. Navigate to the application/website login page 2. Click on the Google icon present on that page for login 3. A prompt will appear. Select ‘Add a New Account’ to add another Google account to sign in 4. Add a new Google account 5. Go to the sign up page of the application and sign up using the new Google account details 6. A prompt will appear. Select ‘Proceed’ or ‘Confirm’ the Google username for signing in	The application should allow you to process the request and direct you to the dashboard/homepage	Fill based on observation	Pass/Fail

Let’s take another example of validating the Response headers, which is mentioned in the above section. The header part consists of ‘metadata,’ including the Content-Type attribute that makes us understand how to interpret the data of the response body. Thus, if the response body consists of JSON data, the content-type attribute in the header will be application/json. And, if there is XML data in the body is XML, the content-type header will be application/xml. You can run the API URL on an automation tool or a framework to execute the test cases and receive the response.

Automating your API Testing

Up until now, we were primarily discussing manual API testing, and the template also contains test cases to execute the steps. But there are ways to automate your API testing test cases to save a considerable amount of time and money. Not only that, but automating test cases for API testing will also decrease accuracy issues by a huge percentage and direct your employees’ manual labor toward other productive business elements. One primary aspect to be mindful of is: when to make the transition from manual to automation testing. It is advised to switch when your test cases are frequently executed and take too much of time in manually executing.

There are numerous API testing tools that support verifying the APIs and collecting relevant output information to extend your QA efforts without giving it much time.

Benefits of Automating API Testing

There are multiple benefits of automating API testing test cases besides saving time, money, and energy:

• Automation offers better test coverage
• Allows for faster bug fixes
• Offers quick response time

How Testsigma Simplifies Automation of API Testing?

Automating API testing takes a lot less time than when it is done manually. But writing test scripts might still require an understanding of programming languages and time. Not to mention the coding would need extended attention if any syntax issue arises. Enter Testsigma, a no-code test automation platform with its intuitive user interface and API testing support. Here are all the ways Testsigma simplifies automating API testing:

• Testsigma tests all API methods and runs parameterized REST API verification on autopilot
• It validates API responses and stores the response data for future reuse
• It offers a no-code API testing option through many NLPs that you can use to request API calls and check their functioning
• The tool’s end-to-end testing capability brings functional UI and API testing together
• Not only APIs, you can also automate your tests for web, mobile, and desktop with Testsigma
• Testsigma is also available as open source and free

Start automating your API tests with Testsigma Open Source

Conclusion

APIs are integral to every modern application, and their testing is far more essential than realized before. This blog explores the widespread possibility of performing API testing. And provides sample test cases for API testing that you can use as a template for your own use. Simply copy the sheet into your system and add API test cases that correspond to your testing requirement. The next phase of the blog talks about automating these test cases using tools. Most of them are code-based and provide huge support in saving time and money. And we further dive into our tool, Testsigma, which also offers API testing without any coding requirement. From integrating it with other third-party tools to executing end-to-end testing incorporating API verification, Testsigma does everything using NLP statements.

Frequently Asked Questions (FAQs)

What is the best way to test API?

You can test APIs manually or automatically. Automating your APIs makes sense if you run your API tests frequently and you see an ROI post automation.Go for automation tools that offer extended capabilities. You can follow the steps as specified in the tools you are using, or you can develop a general series of steps to perform API testing: Understand the API >> Create a test suite >> Analyze the results >> Integrate with DevOps as per your need