API testing differs greatly from User Interface testing as API is designed to integrate two modules in a system or between two systems instead of between a system and an end user to promote communication among the respective modules which is why test execution for APIs must be done with significantly designed test cases and strategies.
Also, where most cases of the user interface testing is done manually, it is impossible to conduct similar testing procedure for APIs and thus specialized tools are needed for API testing which will be discussed in a different post.
API testing can be done in various forms and methods setting up different test scenarios. For conducting structured testing, there is a three step procedure for executing a fundamental API testing process which involves:
- Syntax testing: Syntax testing is executed to check individual operatives as to whether they accept a correct input and reject an incorrect input into the functions.
- Functional Testing: This type of module testing is conducted to check methods and operations for their specific functionality. It determines if the method or operations perform its designated action correctly.
- Test Scenarios: After each individual module and operation has been tested successfully then these methods are strung into one for executing a collaborative end-to-end test scenario.
Non-Functional testing is also an elaborate and necessary testing module for checking characteristics other than functionalities such as:
- Security: This is to check if the API is secure enough and specifically available to only the authorized users with correct permissions.
- Performance and efficiency: APIs operative with web services are tested for performance and efficiency in terms of response time under high and low loads.
- Interoperability and connectivity: It is to check and determine if the API does what it has been created to do that is interacts with and connects separate components as expected and in the intended and acceptable manner.
All of the above mentioned testing procedures are carried out using specialized tools for API testing similar to the tools used for API management and monitoring as an API is not only essential for interaction between different systems but also drives the essential functionalities in any given applicati