What is the strategy that is needed to test an API?

By analyzing the problems faced by the testers, a strategy needs to be formulated for testing the application programming interface.
- The API to be tested would require some environment for it to work. Hence, it is required that all the conditions and prerequisites understood by the tester.
- The next step would be to identify and study its points of entry. The graphical user interfaces would have items like menus, buttons, check boxes, and combo lists that would trigger the event or action to be taken.
- Similarly, for APIs, the input parameters, the events that trigger the API would act as the point of entry. Subsequently, a chief task is to analyse the points of entry as well as significant output items. The input parameters should be tested with the valid and invalid values using strategies like the boundary value analysis and equivalence partitioning.
- The fourth step is to understand the purpose of the routines, the contexts in which they are to be used. Once all this parameter selections and combinations are designed, different call sequences need to be explored.

The steps can be summarized as follows:
- Identify the initial conditions required for testing.
- Identify the parameters i.e. choosing the values of individual parameters.
- Identify the combination of parameters i.e. pick out the possible and applicable parameter combination with multiple parameters.
- Identify the order to make the calls i.e. deciding the order in which to make the calls to force the API to exhibit its functionality.
- Observe the output.