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The Best API Testing Strategy

An API is one of the most important software components in any application. It is the channel used to connect one service to another, providing services that give value to users and driving business processes. If an API breaks, it not only puts a single application to risk but the entire business process built around the API.

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This tells you that it is very important to test APIs. A single test should allow for non-functional testing instead of just triggering and validating individual API calls and their associated responses. This requires an extensive testing strategy between the designers, systems, and implementers to make sure that test cases are tied together for an easy end to end testing. Indeed, you may want to consider the use of API collaboration tools as highlighted in this article to assist with such communication requirements. 


Regardless of what you use to test an API, you need to come up with an API testing strategy that works.

What is an API Test Strategy?

An API test strategy can be described as a high-level description of all the test requirements from which a test plan is derived from with specific test cases and test scenarios. A tester’s first concern should be functional testing. This is made to ensure that the API functions as expected. Here, a tester should ensure that;

  • The API implementation is working according to the requirements specification.
  • The API implementation is working with no bugs.
  • Regressions between releases and code mergers are prevented.

Checking the API Spec

An API can, sometimes, be described as a contract between the server and the client or even between different applications using it. Therefore, before it is implemented, one should make sure that the contract is correct. This is done by inspecting the specification document to make sure that;

  • The API resources and their types reflect the object model correctly.
  • The endpoints are named correctly.
  • No functionality is missing or duplicated.
  • All relationships between resources are reflected correctly in the API.


After successfully validating the API contract, the next step should involve thinking about what to test. Whether you are going to choose automated or manual testing, you will basically employ the same test actions. 

API Test Actions

Test actions are the single actions taken by a test for every API test flow. A test needs to take the following actions with every API request;

  • Verification of HTTP status codes. For example, all requests that are not permitted should return 403 FORBIDDEN while creating a resource returns 201 CREATED.
  • Verification of the response payload. Here, you should make sure that the JSON body is valid and has correct field names, values, and types.
  • Verification of the response headers. This is important because the HTTP server headers affect both the performance and the security of an API.
  • Verification of an application state. This applies to those running manual tests or those with interfaces that can be inspected easily.
  • Verification of the API’s basic performance. For example, a test would be considered as a failed one even if it completed successfully but after taking an unreasonable amount of time.

Test Scenarios

Finally, you will need to come up with some test scenarios for your tests. You can have basic positive tests that check the acceptance criteria of an API and its basic functionality. There is also negative testing where the application is expected to handle problem scenarios with both valid and invalid user input. Negative testing also includes destructive testing where the tester intentionally attempts to break the API to check how strong it would be under severe circumstances. For example, CrackNow should have done destructive testing on their software uploader application to avoid issues like having their accounts compromised in the future.


With such an API testing strategy, you can be guaranteed that your tests will be successful and the API will be ready to face anything thrown at it without any problems. 


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