API Testing

Suppose you are reading a newspaper article on Times of India app and want to share it with your friends online through Twitter. You simply click on the share option and it’s done. We keep getting marvelled of the wonders of Social media apps and are struck with genuine amazement at the speed with which, information is being shared no matter what the distance. But have you ever wondered, what actually ensures this smooth exchange of crazy amounts of data along the information super highways? The answer is API testing.

Challenges in API Testing

Moving forward, to discover the challenges in API testing, it's important to go through different types of testing. When we talk about white-box testing, we concern with internal code and structure of the application. In black-box testing, the tester mainly concern with functionality of the application, they only validate inputs and outputs. But the major fact is that, API testing usually follows white-box testing approach. These are some of the major key consideration which reflects challenges clearly:

  1. There is no such GUI available in the market that tests the application which eventually makes it difficult to provide input values for the system.
  2. Verifying and interpreting the output in different systems is quite problematic for testers.
  3. Testers required Parameter Selection and Categorization to know understand actual conditions.
  4. It is important to test exception handling function.
  5. Profound knowledge of coding is necessary for testers.
  6. API testing must have Parameter Combination, Parameter Selection and Call Sequencing.

API - The Concept and It's Need

API (Application programming interface) works as a facilitating interface for interaction between two disparate software technologies. API testing is a unique variant of software testing, which ensures that the interaction between two applications goes without any glitches. In other words, the testing is done to ensure an error free API for a software product before it is shipped out for delivery. Rule of thumb for such testing is the simple issuance of wide range of requests to the targeted API and determines whether the responses received at various end points are correct or not. The end points can be web services or different databases. API testing is crucial for developers to seamlessly fit new apps into social media tools like Facebook and Instagram. API test also detects lagging of system functions.

API Testing neither uses standard user inputs from keyboard nor any outputs; it simply uses a software application to send a call to API and get a relevant output with system’s response. To bridge an appropriate interaction with API, testing methodology requires an application. To perform testing, these are two key points that helps a lot to test API:

  • Using appropriate testing tool to drive API.
  • Generate or write own code to test the API.

How Api Testing is Performed?

Based on inputs of technology and Market research tools like Forrester, some of the Top dogs in API testing are desktop based. Best among them are Parasoft SOA test and Microsoft Visual Studio.

Here’s a brief outline of some of the practices in API testing, which are currently in vogue:-

Unit Testing: It is primarily used for testing the efficacy of the most basic of individual operations which includes testing of source codes and operating procedures. This approach is highly beneficial during the times of system upgradation. Downside is that we can’t unit test, in an actually deployed environment.

Functional testing: Based on the specifications of the app under test, functional testing chiefly revolves around the main utility of the software. The core functions are examined by the feeding input and the subsequent monitoring of the response.

Load testing: Also known as Stress testing, it involves a thorough evaluation of the software behaviour operating under normal and peak load conditions. This helps in detecting any defects or bugs which might interfere with the smooth functioning of the product. Additionally it helps to check the system response when bombarded with outputs in excess to its capacity.

Runtime Error Detection: In this type of testing, runtime error detection monitor the automation or manual execution tests to get rid from problems like race conditions, exceptions and resource leaks.

Security Testing: This is type software testing which includes penetration testing and fuzz testing to perform API testing and also validating authentication, encryption and access control. Security testing makes system more secure than any other methodology.

Web UI Testing: This type of testing performs end to end integration testing which mainly covers all APIs and enables a team to check GUI items for larger transaction.

Interoperability Testing: This type of testing technique check the conformance of web services interoperability profiles to make a system secure to perform web operations accurately.

Compliance Testing: The compliance testing validates the compliance to WS* standards which are WS-Addressing, WS-Discovery, WS-Federation, WS-Security, WS-Policy and WS-Trust.

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


Application programming interface (API) testing is an identical approach that builds seamless applications that makes work and accessibility more reliable. Correlating and collecting all the above definitions helps testers or a testing team to validate functionality and features more precisely.