Access files in docker image from host machine

I’m trying to write unit tests for an API to a legacy system. The legacy system that is running in Windows are using some big binary files to store its data, and I can not guarantee that the conditions are the same between each run of the unit tests.

I’m wondering if I can somehow can use docker to make sure the binaries are the same between each run.
I’m thinking of running the legacy system in Windows on the host machine, and having the binaries managed in Docker so that they restored between each run.
I’m pretty new to Docker, and I wonder if this is even possible.

The best thing would have been if I could run the legacy system in Docker as well, but it is a GUI application in Windows, and as I understand it, Docker does not support such applications. Or am I wrong?