Add assertion to verify tested data is not pre-existing

Issue: AAH-906

galaxy_ng/tests/functional/cli/test_container_repository_tags.py

@@ -2,6 +2,7 @@
 
 from urllib.parse import urlparse
 
+from pulpcore.client.galaxy_ng.exceptions import ApiException
 from pulp_container.tests.functional.api import rbac_base
 from pulp_container.tests.functional.constants import DOCKERHUB_PULP_FIXTURE_1
 from pulp_smash import cli
@@ -43,6 +44,13 @@ def test_list_container_repository_tags(self):
         image_path = f"{DOCKERHUB_PULP_FIXTURE_1}:manifest_a"
         local_url = "/".join([self.registry_name, f"{image_name}:1.0"])
 
+        # expect the Container Repository Tags not to exist yet
+        with self.assertRaises(ApiException) as context:
+            self.container_repo_tags_api.list(base_path=image_name)
+
+        # Bad request
+        assert context.exception.status == 404
+
         self._push(image_path, local_url, self.user_admin)
 
         response = self.container_repo_tags_api.list(base_path=image_name)