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API Testing Checklist


It's difficult to make a universal API checklist because APIs can be very diverse in their functionality, design, and implementation. It's difficult to make a universal API checklist because APIs can be very diverse in their functionality, design, and implementation. APIs are used across a wide range of applications and industries, and they can have different purposes, requirements, and constraints. Therefore, there's no one-size-fits-all checklist that can cover all the possible scenarios and use cases for API testing. If the API is expected to receive a high volume of requests or handle a large amount of data, load and performance testing becomes critical but if the API is intended for internal use only, and the expected usage is low, load and performance testing may not be a priority. In the case of public APIs, clear and accurate documentation is critical because the APIs are designed to be used by third-party developers and applications. For internal APIs, the documentation may not need to be as comprehensive as public APIs. That is why we will create a small checklist of the most critical checks, you can select the checks that apply to the API you need to test. However, keep in mind that this is a small general checklist, and additional checks may be necessary depending on the specific requirements of the API and the business needs of the organization. One of the principles of testing is Testing Is Context Dependent.

1. Always start with Happy Path

Check the valid Request

  • Check the HTTP method

  • Check the URI/URL

  • Check query parameters

  • Check path parameters

  • Request headers

  • Check the Request body structure

  • Check the Request body values

Check the valid Response

  • Check the HTTP status code

  • Check the Response body structure

  • Check the Response body values

  • Check Response headers

2. Documentation testing (Ensure that the documentation includes all necessary information)

e.g. Examples of valid requests and responses; Examples of responses to invalid requests; Verifying that the request parameters are correct; Verifying that the response structure is correct; Verifying that the response codes and messages are correct; Verifying that the authentication and authorization requirements are correct, etc.

3. Contract Testing (Testing the API against a predefined contract or specification. The contract defines the expected behavior of the API, including the input parameters, expected output, and error handling)

e.g. Test API according to the documentation we tested above.

4. Functional testing (This involves verifying the functionality of an API by testing its endpoints, input validation, output validation, error handling, and other related aspects. The goal of functional API testing is to ensure that the API meets its intended functional requirements and behaves as expected)

e.g. Verify that the API accepts valid data and creates a new resource as expected when sending a valid POST request. Verify that the API returns the correct data when sending a valid GET request. Test whether the API responds correctly to queries with different parameters, such as filtering, sorting, and pagination. Verify that the API returns the expected status codes, such as 200 for a successful response and 404 for a resource not found. Verify that the API accepts valid data and updates the resource as expected when sending a valid PUT request. Verify that the API deletes the resource as expected when sending a valid DELETE request, etc.

5. Security testing (If API requires authentication for all requests)

e.g. Test whether the API is properly authenticating and authorizing users to access resources. This includes testing whether the API rejects unauthorized requests and properly handles authentication failures. Test whether the API is properly validating user input to prevent SQL injection, cross-site scripting (XSS) attacks, and other security vulnerabilities. Test whether the API is properly encrypting and decrypting sensitive data, such as passwords and user credentials. This includes testing whether the API is using secure encryption algorithms and protocols.

6. Performance testing (Ensure that API can handle the expected traffic)

e.g. Load testing with multiple users; Stress testing with maximum load; Endurance testing with prolonged load; Spike testing with sudden load increase; Caching performance; Response time; Error rate, etc.

7. Negative testing (Involves testing an API with invalid or unexpected inputs or scenarios, to ensure that it handles them correctly and responds appropriately.

e.g. Invalid input parameters(request body, headers, query params, path params); Test with missing or invalid data; Test with incorrect data type or format; Test with duplicate data; Test with too much data; Error handling; Security vulnerabilities; Performance under load; Testing edge cases, etc.

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