Changing from SOAP to REST

My team and I are currently working on changing from WSDL/XSD based testing to Swagger/OpenAPIv3Definition JSON files for schemas. I am trying to work through this the same as we did with previous tests and ensure all of our bases are covered.

One thing that is giving me pause is with WSDL/XSD/SOAP tests, I could easily validate that the request matched the schema. With Swagger/JSON and REST tests, there's no real easy (ALT-V or Right Click->Validate) method to do this.

How would one go about doing this sort of validation, to ensure that our data and requests going on match the schema to avoid muddying the waters with positive/happy-day-scenario tests?

I started trying to write a groovy script to validate the request, but haven't mad progress so far. Any/all information appreciated!