Refactor docker-py compatibility tests

* Add which python client is being used to run tests, see "python
  client" below.
* Remove redundate code from test classes
* Update/Add comments to modules and classes

======================================================= test session starts ========================================================
platform linux -- Python 3.10.0, pytest-6.2.4, py-1.10.0, pluggy-0.13.1
python client -- DockerClient
rootdir: /home/jhonce/Projects/go/src/github.com/containers/podman
plugins: requests-mock-1.8.0
collected 33 items

test/python/docker/compat/test_containers.py ...s..............  [ 54%]
test/python/docker/compat/test_images.py ............  [ 90%]
test/python/docker/compat/test_system.py ...  [100%]

Note: Follow-up PRs will verify the test results and expand the tests.

Signed-off-by: Jhon Honce <jhonce@redhat.com>

test/python/docker/compat/common.py

@@ -1,23 +1,92 @@
+"""
+Fixtures and Helpers for unittests.
+"""
+import subprocess
+import sys
+import time
+import unittest
+
+# pylint: disable=no-name-in-module,import-error,wrong-import-order
 from docker import DockerClient
 
+from test.python.docker import PodmanAPI
 from test.python.docker.compat import constant
 
 
 def run_top_container(client: DockerClient):
-    c = client.containers.create(
-        constant.ALPINE, command="top", detach=True, tty=True, name="top"
+    """Run top command in a alpine container."""
+    ctnr = client.containers.create(
+        constant.ALPINE,
+        command="top",
+        detach=True,
+        tty=True,
+        name="top",
     )
-    c.start()
-    return c.id
+    ctnr.start()
+    return ctnr.id
 
 
 def remove_all_containers(client: DockerClient):
+    """Delete all containers from the Podman service."""
     for ctnr in client.containers.list(all=True):
         ctnr.remove(force=True)
 
 
 def remove_all_images(client: DockerClient):
+    """Delete all images from the Podman service."""
     for img in client.images.list():
         # FIXME should DELETE /images accept the sha256: prefix?
         id_ = img.id.removeprefix("sha256:")
         client.images.remove(id_, force=True)
+
+
+class DockerTestCase(unittest.TestCase):
+    """Specialized TestCase class for testing against Podman service."""
+
+    podman: PodmanAPI = None  # initialized podman configuration for tests
+    service: subprocess.Popen = None  # podman service instance
+
+    top_container_id: str = None
+    docker: DockerClient = None
+
+    @classmethod
+    def setUpClass(cls) -> None:
+        super().setUpClass()
+
+        cls.podman = PodmanAPI()
+        super().addClassCleanup(cls.podman.tear_down)
+
+        cls.service = cls.podman.open("system", "service", "tcp:127.0.0.1:8080", "--time=0")
+        # give the service some time to be ready...
+        time.sleep(2)
+
+        return_code = cls.service.poll()
+        if return_code is not None:
+            raise subprocess.CalledProcessError(return_code, "podman system service")
+
+    @classmethod
+    def tearDownClass(cls) -> None:
+        cls.service.terminate()
+        stdout, stderr = cls.service.communicate(timeout=0.5)
+        if stdout:
+            sys.stdout.write("\ndocker-py -- Service Stdout:\n" + stdout.decode("utf-8"))
+        if stderr:
+            sys.stderr.write("\ndocker-py -- Service Stderr:\n" + stderr.decode("utf-8"))
+
+        return super().tearDownClass()
+
+    def setUp(self) -> None:
+        super().setUp()
+
+        self.docker = DockerClient(base_url="tcp://127.0.0.1:8080", timeout=15)
+        self.addCleanup(self.docker.close)
+
+        self.podman.restore_image_from_cache(self.docker)
+        self.top_container_id = run_top_container(self.docker)
+        self.assertIsNotNone(self.top_container_id, "Failed to create 'top' container")
+
+    def tearDown(self) -> None:
+        remove_all_containers(self.docker)
+        remove_all_images(self.docker)
+
+        super().tearDown()