…s,, you can directly use the `response.Header.Get(header)` method.

So instead of using `validateResponseHeaderPatterns` function, instead of using `http.CanonicalHeaderKey` to check if a header exists, you can directly use the `response.Header.Get(header)` method. It automatically handles case-insensitive header names.

Use a switch statement instead of multiple if conditions for validating the HTTP method in the `preProcessTest` function. It will be more concise and easier to read.

Extract the header validation logic from validateResponseHeaders into separate functions for each type of assertion (patterns, `notMatching`, `notPresent`, `ifPresentNotMatching`). 

This will make the code more modular and easier to understand.