How to track API parameters' coverage when doing web service testing?

I am currently using SoapUI to do the web service testing.

My current practice is one test suite for one API, under that are test steps. The steps are for testing different parameters of that API, usually including lots of scenarios(eg. given invalid/null values)

I don't know how I am able to track every API's parameters to make sure they're all covered in the scripts, because usually I'll miss scenarios like two parameters are given at the same time or the parameters get invalid values etc.

I know about JaCoCo, which can track Java Code Coverage. Is there a tool or a solution to this, too? Thank you.