test: add schema evolution

Author: scream4ik

tests/test_schema_evolution.py

@@ -0,0 +1,77 @@
+import pytest
+from pydantic import BaseModel, Field
+from memstate import MemoryStore, InMemoryStorage
+
+
+class UserProfileV1(BaseModel):
+    username: str
+    # the `role` field is missing yet
+
+
+class UserProfileV2(BaseModel):
+    username: str
+    role: str = Field(default="user")
+
+
+class UserProfileV3_Strict(BaseModel):
+    username: str
+    age: int  # a new field without a default value
+
+
+class UserProfileV4(BaseModel):
+    username: str
+
+
+@pytest.fixture
+def memory():
+    return MemoryStore(InMemoryStorage())
+
+
+def test_schema_evolution_adding_field_with_default(memory):
+    memory.register_schema("user", UserProfileV1)
+
+    id_v1 = memory.commit_model(UserProfileV1(username="legacy_user"))
+
+    memory.register_schema("user", UserProfileV2)
+
+    fact_data = memory.storage.load(id_v1)
+    raw_payload = fact_data["payload"]
+
+    user_obj = UserProfileV2(**raw_payload)
+
+    assert user_obj.username == "legacy_user"
+    assert user_obj.role == "user"
+
+    id_v2 = memory.commit_model(UserProfileV2(username="new_user", role="admin"))
+
+    raw_payload_v2 = memory.storage.load(id_v2)["payload"]
+    assert raw_payload_v2["role"] == "admin"
+
+
+def test_schema_breaking_change(memory):
+    memory.register_schema("user", UserProfileV1)
+    id_v1 = memory.commit_model(UserProfileV1(username="young_user"))
+
+    memory.register_schema("user", UserProfileV3_Strict)
+
+    fact_data = memory.storage.load(id_v1)
+
+    with pytest.raises(ValueError) as excinfo:
+        UserProfileV3_Strict(**fact_data["payload"])
+
+    assert "age" in str(excinfo.value)
+    assert "Field required" in str(excinfo.value)
+
+
+def test_loading_rich_data_into_slim_model(memory):
+    memory.register_schema("user", UserProfileV2)
+    rich_id = memory.commit_model(UserProfileV2(username="rich_user", role="admin"))
+
+    memory.register_schema("user", UserProfileV4)
+
+    fact_data = memory.storage.load(rich_id)
+
+    user_obj = UserProfileV4(**fact_data["payload"])
+
+    assert user_obj.username == "rich_user"
+    assert not hasattr(user_obj, "role")