Maven dependencies are cached inside the image, because you don't want to download them multiple times before starting/running the tests, right? :)
Maven command is executed in the maven_runner.sh, that reports back to the docker run setting the appropriate exit code != 0 in case of test failures. This can be used on your CI to decide what to do next on the workflow.
docker build -t karate_docker .
docker run karate_docker
Happy Dockarat'ing!