Checklist while doing API testing

When we say API, we have many things that will comes to our mind, lets quickly look into my checklist to cross check with yours :P

1. Check HTTP Codes and corresponding status for different scenarios
2. Play with Mandatory and Optional fields
3. Resiliency testing — How API is behaving with 3rd party system integration and the API’s behaviour when 3rd party system system is slow or down
4. With / Without Authentication
5. With / Without Authorisation
6. Special characters in each input param
7. Trying to mock and test if we are depending on 3rd party services
8. Contract Testing (if required)

Useful Tools

1. Pact for contract testing
2. Some mocking tools — Wiremock, Mountebank