Add unit tests for mongo repository (#5)

todo/tests/unit/repositories/__init__.py

@@ -0,0 +1 @@
+# Added this because without this file Django isn't able to auto detect the test files

todo/tests/unit/repositories/common/__init__.py

@@ -0,0 +1 @@
+# Added this because without this file Django isn't able to auto detect the test files

todo/tests/unit/repositories/common/test_mongo_repository.py

@@ -0,0 +1,57 @@
+from unittest import TestCase
+from unittest.mock import MagicMock, patch
+from todo.repositories.common.mongo_repository import MongoRepository
+from todo_project.db.config import DatabaseManager
+
+
+class MongoRepositoryTests(TestCase):
+    def test_subclass_without_collection_name_raises_error(self):
+        with self.assertRaises(TypeError) as context:
+
+            class InvalidRepository(MongoRepository):
+                pass
+
+        self.assertIn(
+            "Class InvalidRepository must define a static `collection_name` field as a string.", str(context.exception)
+        )
+
+    def test_subclass_with_invalid_collection_name_raises_error(self):
+        with self.assertRaises(TypeError) as context:
+
+            class InvalidRepository(MongoRepository):
+                collection_name = 123
+
+        self.assertIn(
+            "Class InvalidRepository must define a static `collection_name` field as a string.", str(context.exception)
+        )
+
+    def test_subclass_with_valid_collection_name_passes(self):
+        try:
+
+            class ValidRepository(MongoRepository):
+                collection_name = "valid_collection"
+        except TypeError:
+            self.fail("TypeError raised for a valid subclass with collection_name")
+
+    @patch.object(DatabaseManager, "get_collection")
+    def test_get_collection_initializes_collection(self, mock_get_collection):
+        class TestRepository(MongoRepository):
+            collection_name = "test_collection"
+
+        mock_get_collection.return_value = MagicMock()
+
+        collection = TestRepository.get_collection()
+        mock_get_collection.assert_called_once_with("test_collection")
+        self.assertEqual(TestRepository.collection, collection)
+
+    @patch.object(DatabaseManager, "get_collection")
+    def test_get_collection_uses_cached_collection(self, mock_get_collection):
+        class TestRepository(MongoRepository):
+            collection_name = "test_collection"
+
+        mock_get_collection.return_value = MagicMock()
+
+        TestRepository.get_collection()
+        TestRepository.get_collection()
+
+        mock_get_collection.assert_called_once_with("test_collection")