feat: add more info to validation errors (#1233)

Author: gadomski

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Added
 
 - More permissive schema_uri matching to allow future versions of extension schemas ([#1231](https://github.com/stac-utils/pystac/pull/1231))
+- Better error messages from jsonschema validation ([#1233](https://github.com/stac-utils/pystac/pull/1233))
 
 ### Fixed
 

pystac/validation/stac_validator.py

@@ -210,6 +210,8 @@ def _validate_from_uri(
             msg += f"against schema at {schema_uri}"
 
             best = jsonschema.exceptions.best_match(errors)
+            if best:
+                msg += "\n" + str(best)
             raise STACValidationError(msg, source=errors) from best
 
     def validate_core(

tests/test_item.py

@@ -13,7 +13,7 @@
 
 import pystac
 import pystac.serialization.common_properties
-from pystac import Asset, Catalog, Collection, Item, Link
+from pystac import Asset, Catalog, Collection, Item, Link, STACValidationError
 from pystac.utils import (
     datetime_to_str,
     get_opt,
@@ -636,3 +636,10 @@ def test_pathlib() -> None:
     # This works, but breaks mypy until we fix
     # https://github.com/stac-utils/pystac/issues/1216
     Item.from_file(Path(TestCases.get_path("data-files/item/sample-item.json")))
+
+
+def test_invalid_error_message(item: Item) -> None:
+    item.extra_fields["collection"] = "can't have a collection"
+    with pytest.raises(STACValidationError) as error:
+        item.validate()
+    assert "can't have a collection" in str(error.value)