When you have a running container (via docker.image('foo').run() it's very useful to be able to execute a command directly in the container (eg ansible) and keep with the Jenkinsfile syntax, rather than 'sh' everything

It should be possible to do something like the following:

def con = docker.image('myapp').run()
con.exec('ansible localhost /myapp/yoo.yml')
sh 'make test'
con.stop()

Having this functionality then makes handling testing requiring multiple containers much simpler.