How to use the rocker.core.get_docker_client function in rocker

def test_pull_image(self):
        TEST_IMAGE='alpine:latest'
        docker_client = get_docker_client()

        l = docker_client.images()
        tags = set(chain.from_iterable([i['RepoTags'] for i in l if i['RepoTags']]))
        print(tags)
        if TEST_IMAGE in tags:
            docker_client.remove_image(TEST_IMAGE)
            print('removed image %s' % TEST_IMAGE)
        self.assertTrue(pull_image(TEST_IMAGE))

def setUpClass(self):
        client = get_docker_client()
        self.dockerfile_tags = []
        for distro_version in ['xenial', 'bionic']:
            dockerfile = """
FROM ubuntu:%(distro_version)s

RUN apt-get update && apt-get install x11-utils -y && apt-get clean

CMD xdpyinfo
"""
            dockerfile_tag = 'testfixture_%s_x11_validate' % distro_version
            iof = StringIO((dockerfile % locals()).encode())
            im = client.build(fileobj = iof, tag=dockerfile_tag)
            for e in im:
                pass
                #print(e)
            self.dockerfile_tags.append(dockerfile_tag)