Add tests for PyObjectId (#5)

todo/tests/unit/models/__init__.py

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+# Added this because without this file Django isn't able to auto detect the test files

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

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+# Added this because without this file Django isn't able to auto detect the test files

todo/tests/unit/models/common/test_pyobjectid.py

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+from unittest import TestCase
+from bson import ObjectId
+from pydantic import BaseModel, ValidationError
+
+from todo.models.common.pyobjectid import PyObjectId
+
+
+class PyObjectIdTests(TestCase):
+    def test_validate_valid_objectid(self):
+        valid_id = str(ObjectId())
+        validated = PyObjectId.validate(valid_id)
+        self.assertEqual(validated, ObjectId(valid_id))
+
+    def test_validate_invalid_objectid(self):
+        invalid_id = "invalid_objectid"
+        with self.assertRaises(ValueError) as context:
+            PyObjectId.validate(invalid_id)
+        self.assertIn(f"Invalid ObjectId: {invalid_id}", str(context.exception))
+
+    def test_validate_none(self):
+        self.assertIsNone(PyObjectId.validate(None))
+
+    def test_pydantic_json_schema(self):
+        field_schema = {}
+        PyObjectId.__get_pydantic_json_schema__(field_schema)
+        self.assertEqual(field_schema["type"], "string")
+
+    def test_integration_with_pydantic_model(self):
+        class TestModel(BaseModel):
+            id: PyObjectId
+
+        valid_id = str(ObjectId())
+        instance = TestModel(id=valid_id)
+        self.assertEqual(instance.id, ObjectId(valid_id))
+
+        invalid_id = "invalid_objectid"
+        with self.assertRaises(ValidationError) as context:
+            TestModel(id=invalid_id)
+        self.assertIn(f"Invalid ObjectId: {invalid_id}", str(context.exception))
+
+        try:
+            TestModel(id=None)
+        except ValidationError:
+            self.fail("ValidationError raised for None id")