Changed ansible-test to use docker if available (#99)

Now all ansible-test commands will make use of docker if docker
is detected as present and running. The fallback remains to use
the `--venv` option. This also enables users to test against
any python versions supported by ansible, even if they do not
have it installed locally.

src/tox_ansible/ansible/__init__.py

@@ -11,6 +11,7 @@
 from ..tox_ansible_test_case import ToxAnsibleTestCase
 from ..tox_lint_case import ToxLintCase
 from ..tox_molecule_case import ToxMoleculeCase
+from ..utils import use_docker
 from .scenario import Scenario
 
 LOCAL_CONFIG_FILE = ".config/molecule/config.yml"
@@ -128,29 +129,33 @@ def tox_cases(self):
         # pylint: disable=fixme
         # TODO(ssbarnea): Detect and enable only those tests that do exist
         # to avoid confusing tox user.
-        #
+
+        if use_docker():
+            opts = ["--docker", "default"]
+        else:
+            opts = ["--venv"]
         # We use --venv because otherwise we risk getting errors from the
         # system environment, especially as one of tests performed is
         # 'pip check'.
         ANSIBLE_TEST_COMMANDS: Dict[str, Dict[str, Any]] = {
             "integration": {
-                "args": ["--requirements", "--venv"],
+                "args": ["--requirements", *opts],
                 "requires": "tests/integration",
             },
             "network-integration": {
-                "args": ["--requirements", "--venv"],
+                "args": ["--requirements", *opts],
                 "requires": "tests/network-integration",
             },
             # sanity tests do not need presence of sanity check or even tests
             # folder
-            "sanity": {"args": ["--requirements", "--venv"], "requires": ""},
-            "shell": {"args": ["--requirements", "--venv"]},
+            "sanity": {"args": ["--requirements", *opts], "requires": ""},
+            "shell": {"args": ["--requirements", *opts]},
             "units": {
-                "args": ["--requirements", "--venv"],
+                "args": ["--requirements", *opts],
                 "requires": "tests/unit",
             },
             "windows-integration": {
-                "args": ["--requirements", "--venv"],
+                "args": ["--requirements", *opts],
                 "requires": "tests/windows-integration",
             },
             # special commands (not supported by us yet)

src/tox_ansible/utils.py

@@ -0,0 +1,20 @@
+import subprocess
+from functools import lru_cache
+
+
+@lru_cache()
+def use_docker() -> bool:
+    """Return true if we should use docker."""
+    # docker version command works even if service is not accesible, but
+    # info should pass only if we have a running service.
+    try:
+        result = subprocess.run(
+            ["docker", "info"],
+            check=False,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+        )
+        return result.returncode == 0
+    except FileNotFoundError:
+        pass
+    return False