To build:

docker build -rm -t docker-gradle .

To run:

docker run -rm -v $PWD:/opt/gradle -i -t docker-gradle tasks
docker run -rm -v $PWD:/opt/gradle -i -t docker-gradle test
docker run -rm -v $PWD:/opt/gradle -i -t docker-gradle build

This will run Gradle tasks against an example Gradle + Groovy project in a Docker container.