test minor artifact changes for backward + forward compatability

core/dbt/artifacts/README.md

@@ -33,8 +33,13 @@ All existing resources are defined under `dbt/artifacts/resources/v1`.
 ### Non-breaking changes
 
 Freely make incremental, non-breaking changes in-place to the latest major version of any artifact in mantle (via minor or patch bumps). The only changes that are fully forward and backward compatible are: 
-* Adding a new field with a default
-* Deleting an __optional__ field
+1. Adding a new field with a default
+2. Deleting a field with a default
+  * This is compatible in terms of serialization and deserialization, but still may be lead to suprising behaviour:
+    * For artifact consumers relying on the fields existence (e.g. `manifest["deleted_field"]` will stop working unless the access was implemented safely)
+    * Old code (e.g. in dbt-core) that relies on the value of the deleted field may have surprising behaviour given only the default value will be set when instantiated from the new schema
+
+These types of minor, non-breaking changes are tested by [tests/unit/artifacts/test_base_resource.py::TestMinorSchemaChange](https://github.com/dbt-labs/dbt-core/blob/main/tests/unit/artifacts/test_base_resource.py).
 
 ### Breaking changes
 A breaking change is anything that: 

tests/unit/artifacts/test_base_resource.py

@@ -0,0 +1,57 @@
+from dataclasses import dataclass
+import pytest
+
+from dbt.artifacts.resources.base import BaseResource
+from dbt.artifacts.resources.types import NodeType
+
+
+@dataclass
+class BaseResourceWithDefaultField(BaseResource):
+    field_with_default: bool = True
+
+
+class TestMinorSchemaChange:
+    @pytest.fixture
+    def base_resource(self):
+        return BaseResource(
+            name="test",
+            resource_type=NodeType.Model,
+            package_name="test_package",
+            path="test_path",
+            original_file_path="test_original_file_path",
+            unique_id="test_unique_id",
+        )
+
+    @pytest.fixture
+    def base_resource_new_default_field(self):
+        return BaseResourceWithDefaultField(
+            name="test",
+            resource_type=NodeType.Model,
+            package_name="test_package",
+            path="test_path",
+            original_file_path="test_original_file_path",
+            unique_id="test_unique_id",
+            field_with_default=False,
+        )
+
+    def test_serializing_new_default_field_is_backward_compatabile(
+        self, base_resource_new_default_field
+    ):
+        # old code (using old class) can create an instance of itself given new data (new class)
+        BaseResource.from_dict(base_resource_new_default_field.to_dict())
+
+    def test_serializing_new_default_field_is_forward_compatible(self, base_resource):
+        # new code (using new class) can create an instance of itself given old data (old class)
+        BaseResourceWithDefaultField.from_dict(base_resource.to_dict())
+
+    def test_serializing_removed_default_field_is_backward_compatabile(self, base_resource):
+        # old code (using old class with default field) can create an instance of itself given new data (class w/o default field)
+        old_resource = BaseResourceWithDefaultField.from_dict(base_resource.to_dict())
+        # set to the default value when not provided in data
+        assert old_resource.field_with_default is True
+
+    def test_serializing_removed_default_field_is_forward_compatible(
+        self, base_resource_new_default_field
+    ):
+        # new code (using class without default field) can create an instance of itself given old data (class with old field)
+        BaseResource.from_dict(base_resource_new_default_field.to_dict())