APIs are a set of communication protocols that define how different components should interact. APIs can be architectured in different models and by using different technologies. It comprises of a query, response, and data. APIs are usually invoked by GUI based frontends. As a top API web testing service provider for US, we test API services end to end to ensure a stable system. APIs can also be publically accessed or privately accessed
Unit testing of APIs involves testing a single endpoint in isolation with different parameters. The output or response is measured with the expected results. Unit testing of APIs can be done manually as well as automated.
Once APIs are tested in isolation, i.e unit tested, Integration testing of APIs takes place. Emphasizing on the output of one endpoint as an input to another. Integration testing can be done with 3rd party APIs as well
Performance testing of APIs takes into account the amount of stress i.e multiple requests, low latency, corrupted database, etc, which your API system can deal with. Performance testing is best done with automated test cases.