Currently, the MockSlingHttpServletRequest class is set up to mock query parameters only. It assumes that all request parameters are Strings. It does not track things like contentType of each parameter.
I've prototyped some changes to the code in order to allow the mocking of HTML form submissions (including file uploads). I'd like to submit a PR with those changes.
I'm raising this issue for discussion before generating the PR in case there is any other ongoing work that I'm not aware of or if there are objections to the idea.
If you want to preview the changes ahead of the PR, they are in a fork of the code available here: https://github.com/rmcdouga/sling-org-apache-sling-servlet-helpers