Add test scaffold for docker_image_availability.py

The intention is to set a starting point and let another team member
work on the code to gain experience with tests.

roles/openshift_health_checker/openshift_checks/docker_image_availability.py

@@ -15,6 +15,9 @@ class DockerImageAvailability(OpenShiftCheck):
 
     skopeo_image = "openshift/openshift-ansible"
 
+    # FIXME(juanvallejo): we should consider other possible values of
+    # `deployment_type` (the key here). See
+    # https://github.com/openshift/openshift-ansible/blob/8e26f8c/roles/openshift_repos/vars/main.yml#L7
     docker_image_base = {
         "origin": {
             "repo": "openshift",
@@ -62,9 +65,15 @@ class DockerImageAvailability(OpenShiftCheck):
 
     def required_images(self, task_vars):
         deployment_type = get_var(task_vars, "deployment_type")
+        # FIXME(juanvallejo): we should handle gracefully with a proper error
+        # message when given an unexpected value for `deployment_type`.
         image_base_name = self.docker_image_base[deployment_type]
 
         openshift_release = get_var(task_vars, "openshift_release")
+        # FIXME(juanvallejo): this variable is not required when the
+        # installation is non-containerized. The example inventories have it
+        # commented out. We should handle gracefully and with a proper error
+        # message when this variable is required and not set.
         openshift_image_tag = get_var(task_vars, "openshift_image_tag")
 
         is_containerized = get_var(task_vars, "openshift", "common", "is_containerized")
@@ -104,6 +113,8 @@ class DockerImageAvailability(OpenShiftCheck):
         if result.get("failed", False):
             return []
 
+        # FIXME(juanvallejo): wrong default type, result["info"] is expected to
+        # contain a dictionary (see how we call `docker_info.get` below).
         docker_info = result.get("info", "")
         return [registry.get("Name", "") for registry in docker_info.get("Registries", {})]
 

roles/openshift_health_checker/test/docker_image_availability_test.py

@@ -0,0 +1,28 @@
+import pytest
+
+from openshift_checks.docker_image_availability import DockerImageAvailability
+
+
+@pytest.mark.xfail(strict=True)  # TODO: remove this once this test is fully implemented.
+@pytest.mark.parametrize('task_vars,expected_result', [
+    (
+        dict(
+            openshift=dict(common=dict(
+                service_type='origin',
+                is_containerized=False,
+            )),
+            openshift_release='v3.5',
+            deployment_type='origin',
+            openshift_image_tag='',  # FIXME: should not be required
+        ),
+        {'changed': False},
+    ),
+    # TODO: add more parameters here to test the multiple possible inputs that affect behavior.
+])
+def test_docker_image_availability(task_vars, expected_result):
+    def execute_module(module_name=None, module_args=None, tmp=None, task_vars=None):
+        return {'info': {}}  # TODO: this will vary depending on input parameters.
+
+    check = DockerImageAvailability(execute_module=execute_module)
+    result = check.run(tmp=None, task_vars=task_vars)
+    assert result == expected_result