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API Testing: The Heart of Functional Testing

An API provides much of the functional capabilities in complex software systems.

Most customers are accustomed to interacting with a graphical user interface on the computer. But, many do not realize that much of the functionality of a program comes from APIs in the operating system or the program’s dynamic-link libraries (DLL).

When the business logic or core functionality is exposed via an API call and you want to find functional bugs sooner, then API testing can provide additional value in your overall test strategy. API testing can start even before the user interface is complete, so functional capabilities can be tested while designers are hashing out the “look and feel.” While API testing will not replace testing through the user interface, it can augment your test strategy and provide a solid foundation of automated tests that increase your confidence in the functional quality of your product.

At EuroSTAR 2013 BJ Rollison gave an excellent presentation on API testing that is well worth watching.

Slide share: http://www.slideshare.net/EuroSTARConference/bj-rollison-slides

YouTube: https://www.youtube.com/watch?v=uxQ04SnJ0o4


  • What is API Testing?
  • Why do API testing?
  • The difference between Unit and API tests
  • How to approach API testing
  • Types of bugs testing will find



BJ Rollison, Software Test Architect for Microsoft.
Mr. Rollison started working for Microsoft in 1994, becoming one of the leading experts of test architecture and execution at Microsoft. He also teaches software testing courses for the University of Washington, and sits on the advisory board for testing certification at the University of Washington, the University of California Extension Santa Cruz, and Lake Washington Technical College.
BJ Rollison
BJ Rollison runs a successful consulting practice built on his more than twenty-five years of experience in the software industry. His career at Microsoft began on the Windows 95 team and ended on the Windows Phone team.

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