You can always write a stand alone python tool that pretends that it is a browser, does the GET, confirms that the form looks right, gathers the cookies or other CSRF token souces, and does the POST, including attaching the uploaded data parts. But since this requires dipping into HTTP and HTML further than most people go, it has the potential to be more complicated than what you are testing. Perhaps someone has already done this and will comment.
Of course this doesn't test any browser JavaScript that you are using.
Another approach, probably even more complex, is to add to your favorite browser(s) the ability to script the filling of upload fields.
There are engines that allow you to script clicking and typing on a desktop, but I have no experience with them, and that sounds fragile to me, since, for example, FireFox auto updates and where things are changes.
Bill