[phpMyAdmin Developers] Docker testing and development

I've been trying to do some work on the Docker container we distribute and I've been having a little trouble with sorting out how to do test deployments. Probably it's just me not being familiar with Docker until now.

I know how to run the official phpMyAdmin image with `docker run` like:

docker run --name myadmin -d -e PMA_ARBITRARY=1 -p 8080:80

phpmyadmin/phpmyadmin

I know I can run my own registry server on port 5000, but I don't know how to modify Dockerfile on my own server or any other way to test changes to the image before I push them to Github.

For some reason, Google isn't helping at all with my search.

Does anyone have any suggestion?