[DPE-4494] add unit tests for revision checker (#421)

# Issue
Code for version check has no unit tests. This is a requirement before
publishing as a package

# Solution
Add unit tests for version check

src/version_check.py

@@ -128,7 +128,7 @@ def get_invalid_versions(self) -> List[Tuple[str, int]]:
                 for relation in self.charm.model.relations[relation_name]:
                     related_version = relation.data[relation.app][VERSION_CONST]
                     if int(related_version) != self.version:
-                        invalid_relations.append((relation.app.name, related_version))
+                        invalid_relations.append((relation.app.name, int(related_version)))
         except KeyError:
             raise NoVersionError(f"Expected {relation.app.name} to have version info.")
 

tests/unit/test_version_check.py

@@ -0,0 +1,93 @@
+# Copyright 2024 Canonical Ltd.
+# See LICENSE file for licensing details.
+import unittest
+from unittest.mock import patch
+
+from ops.testing import Harness
+
+from charm import MongodbOperatorCharm
+from version_check import DEPLOYMENT_TYPE, VERSION_CONST, NoVersionError
+
+from .helpers import patch_network_get
+
+CHARMHUB_DEPLOYMENT = "ch"
+LOCAL_DEPLOYMENT = "local"
+RELATION_TO_CHECK_VERSION = "sharding"
+CHARM_VERSION = 123
+VALID_VERSION = CHARM_VERSION
+INVALID_VERSION = 456
+APP_0 = "APP_0"
+APP_1 = "APP_1"
+APP_2 = "APP_2"
+
+
+class TestCharm(unittest.TestCase):
+    @patch("charm.get_charm_revision")
+    @patch_network_get(private_address="1.1.1.1")
+    def setUp(self, get_charm_revision):
+        get_charm_revision.return_value = CHARM_VERSION
+        self.harness = Harness(MongodbOperatorCharm)
+        self.addCleanup(self.harness.cleanup)
+        self.harness.begin()
+
+    def add_invalid_relation(self, deployment=LOCAL_DEPLOYMENT):
+        rel_id = self.harness.add_relation(RELATION_TO_CHECK_VERSION, APP_0)
+        self.harness.add_relation_unit(rel_id, f"{APP_0}/0")
+        self.harness.update_relation_data(
+            rel_id,
+            f"{APP_0}",
+            {VERSION_CONST: str(INVALID_VERSION), DEPLOYMENT_TYPE: deployment},
+        )
+
+    def add_valid_relation(self, deployment=LOCAL_DEPLOYMENT):
+        rel_id = self.harness.add_relation(RELATION_TO_CHECK_VERSION, APP_1)
+        self.harness.add_relation_unit(rel_id, f"{APP_1}/0")
+        self.harness.update_relation_data(
+            rel_id,
+            f"{APP_1}",
+            {VERSION_CONST: str(VALID_VERSION), DEPLOYMENT_TYPE: deployment},
+        )
+
+    def add_relation_with_no_version(self):
+        rel_id = self.harness.add_relation(RELATION_TO_CHECK_VERSION, RELATION_TO_CHECK_VERSION)
+        self.harness.add_relation_unit(rel_id, f"{APP_2}/0")
+
+    def test_get_invalid_versions(self):
+        """Verifies that get invalid versions returns the expected content."""
+        # case one: retrieves invalid versions + valid
+        self.add_invalid_relation()
+        self.add_valid_relation()
+        invalid_version = self.harness.charm.version_checker.get_invalid_versions()
+        assert invalid_version == [(APP_0, INVALID_VERSION)]
+
+        # case two: missing version info
+        self.add_relation_with_no_version()
+        with self.assertRaises(NoVersionError):
+            self.harness.charm.version_checker.get_invalid_versions()
+
+    def test_get_version_of_related_app(self):
+        """Verifies that version checker can retrieve integrated application versions."""
+        # case one: get version
+        self.add_invalid_relation()
+        version = self.harness.charm.version_checker.get_version_of_related_app(APP_0)
+        assert version == INVALID_VERSION
+
+        # case two: missing version info
+        self.add_relation_with_no_version()
+        with self.assertRaises(NoVersionError):
+            self.harness.charm.version_checker.get_version_of_related_app(APP_2)
+
+    def test_is_related_app_locally_built_charm(self):
+        """Verifies that version checker can retrieve integrated application deployment types."""
+        # case one: local deployment
+        self.add_valid_relation(deployment=LOCAL_DEPLOYMENT)
+        assert self.harness.charm.version_checker.is_local_charm(APP_1)
+
+        # case two: charmhub deployment
+        self.add_invalid_relation(deployment=CHARMHUB_DEPLOYMENT)
+        assert not self.harness.charm.version_checker.is_local_charm(APP_0)
+
+        # case three: missing version info
+        self.add_relation_with_no_version()
+        with self.assertRaises(NoVersionError):
+            self.harness.charm.version_checker.is_local_charm(APP_2)