add more tests to validate MLM fields disallowed under Asset

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 - Use JSON `$schema` version `2019-09` to allow use of `unevaluatedProperties` for stricter validation of MLM fields.
+- Explicitly disallow `mlm:name`, `mlm:input`, `mlm:output` and `mlm:hyperparameters` at the Asset level.
+  These fields describe the model as a whole and should therefore be defined in Item properties.
 - Moved `norm_type` to `value_scaling` object to better reflect the expected operation, which could be another
   operation than what is typically known as "normalization" or "standardization" techniques in machine learning.
 - Moved `statistics` to `value_scaling` object to better reflect their mutual `type` and additional

tests/test_schema.py

@@ -68,27 +68,50 @@ def test_mlm_no_undefined_prefixed_field_item_properties(
     ["item_raster_bands.json"],
     indirect=True,
 )
+@pytest.mark.parametrize(
+    ["test_field", "test_value"],
+    [
+        ("mlm:unknown", "random"),
+        ("mlm:name", "test-model"),
+        ("mlm:input", []),
+        ("mlm:output", []),
+        ("mlm:hyperparameters", {}),
+    ]
+)
 def test_mlm_no_undefined_prefixed_field_asset_properties(
     mlm_validator: STACValidator,
     mlm_example: Dict[str, JSON],
+    test_field: str,
+    test_value: Any,
 ) -> None:
     mlm_data = copy.deepcopy(mlm_example)
     mlm_item = pystac.Item.from_dict(mlm_data)
     pystac.validation.validate(mlm_item, validator=mlm_validator)  # ensure original is valid
-
     assert mlm_data["assets"]["weights"]  # type: ignore
-    mlm_data["assets"]["weights"]["mlm:unknown"] = "random"  # type: ignore
+
+    mlm_data = copy.deepcopy(mlm_example)
+    mlm_data["assets"]["weights"][test_field] = test_value  # type: ignore
     with pytest.raises(pystac.errors.STACValidationError) as exc:
         mlm_item = pystac.Item.from_dict(mlm_data)
         pystac.validation.validate(mlm_item, validator=mlm_validator)
     assert len(exc.value.source) == 1  # type: ignore
     schema_error = exc.value.source[0]  # type: ignore
-    assert "mlm:unknown" in schema_error.instance
+    assert test_field in schema_error.instance
     assert schema_error.schema["description"] in [
         "Fields that apply only within an Asset.",
         "Schema to validate the MLM fields permitted only under Assets properties."
     ]
 
+
+@pytest.mark.parametrize(
+    "mlm_example",
+    ["item_raster_bands.json"],
+    indirect=True,
+)
+def test_mlm_allowed_field_asset_properties_override(
+    mlm_validator: STACValidator,
+    mlm_example: Dict[str, JSON],
+) -> None:
     # defined property allowed both at the Item at the Asset level
     mlm_data = copy.deepcopy(mlm_example)
     mlm_data["assets"]["weights"]["mlm:accelerator"] = "cuda"  # type: ignore