SQA interview question 9 - What is the best strategy for API testing?

The easiest approach for API (Application Programming Interface) testing is to develop based on API documentation the collection of software functions and procedures, called API calls, run a suite of API calls and check the results. A high level strategy for API Testing would be Equivalence Class Partitioning method. This method helps QA Tester to derive test cases by identifying the classes of input or output conditions. The rule of thumb is that each member in the class causes the same kind of behavior of the application under test. The Equivalence partitioning appoach creates sets of inputs or outputs that are handled in the same way by the application. In other words, QA Tester can construct a set of of input arguments and for each one determine, what the expected return value should be. For inexperienced tester equivalence partitioning looks like boundary condition testing, but there is a difference and can be used together. To identify test the classes for API testing QA Tester could use arguments type, for example boolean, numeric or text string.