API Testing

What is API?

Abbreviated as API, Application Programming Interface enables communication and data exchange between two separate software systems. A software system implementing an API contains functions and runs routines, which can be executed by another software system. Application Programming Interface (API) mainly concentrates on the business logic layer of the software architecture and it is not focused on or is concerned about the look and feel of the application. Additionally, in computer programming, an Application Programming Interface (API) is a set of subroutine definitions, protocols, and tools for building application software. It is a set of clearly defined methods of communication between various software components. Though APIs are integral part of our interconnected way of life, they are not always tested and executed by proficient developers and testers, and even if testing is performed on them, it is not done thoroughly. Furthermore, APIs are used in programming Graphical User Interface (GUI) components and it makes it possible to quickly create prerequisites for future test cases. In short, a good API makes it easier to develop a program by providing all the building blocks, which are then put together by a programmer.

What is API Testing?

The API Testing is performed for the system, which has a collection of API that ought to be tested. API testing is a type of software testing that involves testing Application Programming Interfaces (APIs) directly and as part of integration testing to determine whether they meet expectations for functionality, reliability, performance, and security. Since APIs lack a GUI, API testing is performed at the message layer. Moreover, API testing is now considered a critical part of automating testing as it now serves as the primary interface to application logic and because GUI tests are difficult to maintain with the short release cycles and frequent changes commonly used with Agile software development and DevOps. Hence, while executing the process of testing the following factors are looked at by the team of testers in API testing:

  • The boundary conditions explored to ensure that the test harness varies parameters of the API calls in ways that verify functionality and expose failures.
  • More value added parameter combinations to verify the calls with two or more parameters are generated.
  • Behaviour of the API is verified, which is considering the external environment conditions such as files, peripheral devices, and so forth.
  • Verifying the Sequence of API calls and check if the API's produce useful results from successive calls.

Types of API Testing:

APIs or Application Programming Interfaces are responsible for connecting the world with each other. It is one of the most important quality of a software or application that should be tested thoroughly to ensure that the application is performing and functioning properly. A good API makes it easier to develop a computer program by providing all the building blocks, which are then put together by the programmer. An API specification can take many forms, but often includes specifications for routines, data structures, object classes, variables or remote calls. There are many different types of APIs for operating systems, applications or websites, which have different testing needs and require tests of various kinds. Therefore, to resolve all these testing requirements following types of tests are performed during API testing:

Interoperability Testing: This is performed on SOAP only, it checks the conformance to web service interoperability profiles.
  1. Unit Testing: Here the testing is executed to test the functionality of individual operations.
  2. Functional Testing: Testing the functionality of broader scenarios, often using unit tests as the building blocks for end to end tests. It includes test case definition, execution, validation, and regression testing.
  3. Load Testing: Validating the functionality and performance under load, often by reusing functional test cases.
  4. Runtime Error Detection: Here the execution of automated or manual test is monitored, to expose problems such as race condition, exceptions and resource leaks.
  5. Security Testing: This includes penetration testing and fuzz testing. Moreover, it validates the authentication, encryption and access control.
  6. Web UI Testing: This type of testing is performed as part of end-to-end integration testing that also covers APIs and enables teams to validate GUI items in the context of the layer transaction.
  7. Interoperability Testing:: This is performed on SOAP only, it checks the conformance to web service interoperability profiles.

Why to Test APIs?

API testing is one of the most beneficial form of testing performed on software and applications. Testers and developers several times don’t understand its importance and tend to avoid it, however, if they want their application to perform and function as well as be reliable and secure, then they should make sure that their API is test thoroughly. API makes it easier for developers to use certain technologies in building applications. Moreover, by abstracting the underlying implementations and only exposing objects or actions the developer needs, an API simplifies programming.

The API is what provides value to the application. Its main aim is to make the mobile devices smart and to streamline business processes. If any API does not work efficiently and effectively, it will never be adopted, regardless whether it is a free and open API or one that charges per call or group of calls. If an API breaks because errors were not detected, it could not only break a single application but also affect a chain of business processes hinged to it. Additionally, there are several areas of an application that can be examined with API testing, such as authentication, setting up new entities within the application, unit testing, infrastructure, security and more. Other reasons for testing API are:

  1. Test Quality: Iterating on API test will make the application stronger and more comprehensive, which will benefit the team in the long term, raise the product quality and will decrease the number of faults that were to be found in the future.
  2. Test Coverage: Performing API testing during application development can reveal issues with API, server, other services, networks, and more, which may not be easily discovered or solved after deployment of the application.
  3. Test Reuse: One of the best reasons for creating API tests in the early stages is the rewards it provides after its deployment, as the bulk of the tests are already taken care by it. Moreover, with the reuse of API tests across development lifecycle, one can facilitate collaboration among teams and provide a more comprehensive and accurate testing canon.

Benefits of Testing APIs:

From the above discussion we can easily understand that API testing is an extremely important type of testing. It significance is immense as API testing not only ensures the quality, functionality, effectiveness, and performance of the software and application, but also validates its reliability and security. With its assistance, developers can easily develop an application and can copy or paste a file from one location to another without understanding the file system operations occurring behind the scenes. Other benefits of testing APIs are mentioned below:

  • With the assistance of API testing one can improve the test cycle coverage, as Quality Assurance (QA) engineers use best practises for API to test scenarios that are most likely to occur.
  • Automated API tests use less code than functional GUI test, which leads to more efficient test coverage.
  • The improved test coverage results in reduced testing cost.
  • API testing encourages collaborations.
  • Testing and development are performed simultaneously.
  • API testing makes it possible to quickly create prerequisites for future test cases.
  • It can be easily integrated with GUI.

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Tools for API Testing

  1. Eclipse SDK tool - Automated API Testing
  3. Runscope
  4. Parasoft SOA Test and Development testing platform
  5. IBM Rational Test Workbench
  6. HP Unified functional testing tool
  7. Microsoft Visual Studio
  8. Smartbear
  9. CTESK
  10. Curl

API Testing Infographics:

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API Testing


Application Programming Interface (API) is the brain that connects the world. It is the set of tools, protocols, standards and code that glues the digital world together. A good API is the secret to testing earlier that is helpful in finding problems earlier in the Software Development Life Cycle (SDLC), which further prevents delays, saves time, ensures the efficiency of the conducted tests and makes the process of testing easier. It is API that provides value to the application and ensure that it performs and functions perfectly. The APIs may be for a web-based system, operating system, database system, computer hardware, or software library Moreover, software engineers conduct API testing, which further validates the quality, reliability, and security of the software. Also, thorough API tests suites are a simple and more convenient way to run through a series of checks after a build and they are generally straightforward to create, automate, and maintain. Some examples of different types of APIs are POSIX, Microsoft Windows API, the C++ Standard Template Library and Java APIs. Therefore, to ensure that a software performs effectively and is of superior quality, software engineers, developers and testers, all should perform thorough API testing, which will help them reduce the time and cost of testing as well as make the end product exceptionally great.

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