add unit tests

tests/unit/test_charm.py

@@ -22,6 +22,7 @@
 from charms.data_platform_libs.v0.data_interfaces import DatabaseRequiresEvents
 
 CLUSTER_ALIAS = "cluster"
+MONGOS_SOCKET_URI_FMT = "%2Fvar%2Fsnap%2Fcharmed-mongodb%2Fcommon%2Fvar%2Fmongodb-27018.sock"
 
 
 class TestCharm(unittest.TestCase):
@@ -32,9 +33,7 @@ def setUp(self, *unused):
             # related to duplicated events.
             delattr(DatabaseRequiresEvents, f"{CLUSTER_ALIAS}_database_created")
             delattr(DatabaseRequiresEvents, f"{CLUSTER_ALIAS}_endpoints_changed")
-            delattr(
-                DatabaseRequiresEvents, f"{CLUSTER_ALIAS}_read_only_endpoints_changed"
-            )
+            delattr(DatabaseRequiresEvents, f"{CLUSTER_ALIAS}_read_only_endpoints_changed")
         except AttributeError:
             # Ignore the events not existing before the first test.
             pass
@@ -143,3 +142,14 @@ def test_status_shows_mongos_waiting(self):
         self.harness.add_relation("cluster", "config-server")
         self.harness.charm.on.update_status.emit()
         self.assertTrue(isinstance(self.harness.charm.unit.status, WaitingStatus))
+
+    @patch_network_get(private_address="1.1.1.1")
+    def test_mongos_host(self):
+        """TBD."""
+        self.harness.charm.app_peer_data["external-connectivity"] = json.dumps(False)
+        mongos_host = self.harness.charm.get_mongos_host()
+        self.assertEqual(mongos_host, MONGOS_SOCKET_URI_FMT)
+
+        self.harness.charm.app_peer_data["external-connectivity"] = json.dumps(True)
+        mongos_host = self.harness.charm.get_mongos_host()
+        self.assertEqual(mongos_host, "1.1.1.1")