An API(Application Programming Interface) allows data exchange from one software to another. Every application nowadays majorly relies on APIs. Hence, API testing is critical and the product has to be tested thoroughly before rolling out to the end user.
It is the software testing practice that tests the APIs directly to ascertain if they meet the requirements for performance, security, functionality and dependability. An API is worthless if it can’t be depended upon, hence testing to validate its implementation is key. An API Test is a set of testing activities that consists of sending calls to the API, getting the result, and validating the response of the system against the definite input parameters. This is done to ensure that the API does what it is supposed to perform, manages the load, works across browsers/ OSs and devices.
Image from https://www.tiempodev.com
Types of API Testing
Validation testing is one of the steps in the development process. It verifies the aspects of the product, behavior and efficiency to validate the API.
Functional testing is a test of specific functions within the codebase. These tests are run to ensure that the API functions are within the expected parameters and errors are handled properly, when the results are outside of the expected parameters.
UI testing is specifically concerned with the function of the UI for the API and its integral parts, whether that interface relies upon command-line endpoint calls or graphical in nature. It focuses more on the interface which ties into the API rather than the API itself. It provides an overview of the health, usability, and efficiency of both, the front and back ends.
Load testing is typically done after the completion of a specific unit or the whole codebase. Load testing monitors the app's performance at both normal and peak conditions. The test is in place to safeguard the effortless performance functioning of the software under real-life conditions.
5. Security Testing
This testing ensures that the API implementation is secure form external threats. Security testing generally encompasses penetration and fuzz testing which works to authenticate encryption and access control for the user. It also entails additional steps including validation of encryption methodologies and validating the design of the access control solution for the API.
6. Runtime/ Error Detection
This type of test is entirely concerned with the actual running of the API. This includes the implementation of manual or automated tests that work to expose glitches. Examples are resource leaks, exceptions, etc.
7. Penetration Testing
It works as a simulated attack against your computer. This is an important test as it operates to find valid weaknesses that an attacker can take advantage of when the system is most vulnerable. In this type of test, the API is attacked by someone who has limited working knowledge of the API itself in order to assess the threat vector from an outside perspective. These attacks can be limited to certain functions, resources, or processes, or can target the entirety of the API and its constituent parts.
8. Fuzz Testing
In fuzz testing, a vast amount of random data (referred to as "noise" or "fuzz") will be input into the system to detect any forced crashes or negative behaviors. This technique tests the API’s limits to prepare for the "worst-case scenarios."
9. Interoperability and WS Compliance Testing
It is only applicable for SOAP APIs. It generally checks for two fields of function. First: Interoperability between SOAP APIs is checked to examine whether the software can intermingled with other components without any compatibility issues. Second: compliance is checked to make sure standards like WS-Discovery, WS-Addressing, WS-Federation, WS-Security, WS-Policy, and WS-Trust are properly utilized and maintained.