What are the different types of API testing?

API is a part of integration testing to check whether the API meets expectations in terms of functionality, reliability, performance, and security of applications.
Unit testing: To test the functionality of individual operation
Functional testing: To test the functionality of broader scenarios by using a block of unit test results tested together
Load testing: To test the functionality and performance under load
Runtime/Error Detection: To monitor an application to identify problems such as exceptions and resource leaks
Security testing: To ensure that the implementation of the API is secure from external threats
UI testing: It is performed as part of end-to-end integration tests to make sure every aspect of the user interface functions as expected
Interoperability and WS Compliance testing: Interoperability and WS Compliance Testing is a type of testing that applies to SOAP APIs. Interoperability between SOAP APIs is checked by ensuring conformance to the Web Services Interoperability profiles. WS-* compliance is tested to ensure standards such as WS-Addressing, WS-Discovery, WS-Federation, WS-Policy, WS-Security, and WS-Trust are properly implemented and utilized
Penetration testing: To find vulnerabilities of an application from attackers
Fuzz testing: To test the API by forcibly input into the system in order to attempt a forced crash