fix disallowing undefined mlm-prefixed fields (fixes #41)

CHANGELOG.md

@@ -20,7 +20,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - n/a
 
 ### Fixed
-- n/a
+- Fix check of disallowed unknown/undefined `mlm:`-prefixed fields
+  (fixes [#41](https://github.com/stac-extensions/mlm/issues/41)).
 
 ## [v1.3.0](https://github.com/stac-extensions/mlm/tree/v1.3.0)
 

json-schema/schema.json

@@ -314,7 +314,7 @@
       },
       "$comment": "Allow properties not defined by MLM prefix to allow combination with other extensions.",
       "patternProperties": {
-        "^(?!dlm:)": {}
+        "^(?!mlm:)": {}
       },
       "additionalProperties": false
     },

tests/test_schema.py

@@ -27,6 +27,29 @@ def test_mlm_schema(
     assert SCHEMA_URI in validated
 
 
+@pytest.mark.parametrize(
+    "mlm_example",
+    ["item_raster_bands.json"],
+    indirect=True,
+)
+def test_mlm_no_undefined_prefixed_field(
+    mlm_validator: STACValidator,
+    mlm_example: Dict[str, JSON],
+) -> 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
+
+    mlm_data["properties"]["mlm:unknown"] = "random"
+    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 all(
+        field in str(exc.value.source)
+        for field in ["mlm:unknown", "^(?!mlm:)"]
+    )
+
+
 @pytest.mark.parametrize(
     "mlm_example",
     ["item_raster_bands.json"],