API Testing – A Quick Guide on the Basics

API Testing – A Quick Guide on the Basics

What is API? 

API stands for Application Programming Interface, which basically helps in transmitting data from one software to another. It specifies how one software program should communicate with another software program. API allows two software applications to connect with each other and serves as an interface between them.

API testing, like other types of testing, aims to find bugs that are caused by inconsistencies or deviations from intended behavior.

What is API testing?

API testing is a sort of software testing in which application programming interfaces are evaluated to see if they meet functional, reliability, performance, and security requirements. API testing is done at the Business Layer. Business logic processing and all interactions between the User Interface (UI) and the database take place at the business layer.

How to perform API testing?

  • Review of API Specifications: The first step is to write down the API testing specifications. What is the function? What are some of the API's features? How will the application's workflow work? Which integrations does the API support?  This will aid you in the planning of tests as well as the testing process itself.
  • Establishing a Test Environment: The next step is to build up a testing environment with the needed set of API parameters. This entails setting up the database and server to meet the application's needs.
  • Integrating Data from Applications: You must integrate your application data with the API tests in this stage to confirm that the API works as intended across all potential input configurations.
  • Choosing an API Test Type: You must determine what you want to test your API for after you've established the testing limits and requirements. Functionality testing, validation testing, load testing, security testing, end-to-end testing, fuzz testing, and many other types of API tests are available.

Types of API Testing:

  1. Unit Test: Unit testing is the process of evaluating the functionality of a single operation.
  2. Functional testing: Using a block of unit test results that are tested together to test the functioning of bigger scenarios.
  3. Load Test: To put the functionality and performance of the system to the test.
  4. Runtime/Error Detection: Keeping an eye on an application to spot issues like exceptions and resource leakage.
  5. Security Test: To guarantee that the implementation is safe from external attacks.
  6. UI testing: It's done as part of end-to-end integration testing to ensure that every piece of the user interface works as it should.
  7. Interoperability and WS Compliance testing: Conformance to the Web Services Interoperability profiles is used to ensure interoperability between SOAP APIs.
  8. Penetration Test: To protect an application from being exploited by attackers by identifying its vulnerabilities.
  9. Fuzz testing entails forcing data into the system in order to simulate a forced crash.


  • You do not have to wait for other teams to finish developing the entire application to begin API testing. Once the logic has been developed, tests may be built to evaluate the correctness of answers and data.
  • API modifications are less common, although API definition files can often aid in the creation of quick refactoring tests.
  • When tests fail, we can pinpoint the specific location of the flaw in the system. This cuts down on the time it takes to track defects across releases, integrations, and even team members.
  • Running more tests means you'll identify more errors in less time, and you'll be able to fix them right away.

Best Practices:

  • Always begin by categorizing test cases into types.
  • Give examples of what the APIs should be called.
  • Specific API criteria should be specified.
  • Separate the tests from one another.
  • Pay special attention to the various processes—in the long run, well-executed tests are the best.


API testing has a few drawbacks:

  • Parameter Combination, Parameter Selection, and Call Sequencing are the three main issues in Web API testing.
  • For testers, coding knowledge is required.
  • There is no graphical user interface to test the application, making it impossible to provide input values.
  • You must test the exception handling function.
  • It's a bit tough for testers to validate and verify the results in a separate system.

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