Merge pull request #35 from fishtown-analytics/dont_best_match

Do not use jsonschema.best_match because it obscures the errors

hologram/__init__.py

@@ -956,6 +956,6 @@ def _get_field_type_name(field_type: Any) -> str:
     def validate(cls, data: Any):
         schema = _validate_schema(cls)
         validator = jsonschema.Draft7Validator(schema)
-        error = jsonschema.exceptions.best_match(validator.iter_errors(data))
+        error = next(iter(validator.iter_errors(data)), None)
         if error is not None:
             raise ValidationError.create_from(error) from error

tests/test_union.py

@@ -1,7 +1,8 @@
 import pytest
 
 from dataclasses import dataclass
-from typing import Union, Optional, List
+from typing import Union, Optional, List, Dict, Any
+import re
 
 from hologram import JsonSchemaMixin, ValidationError
 
@@ -77,3 +78,20 @@ def test_long_union_decoding():
         except ValidationError as exc:
             str(exc)
             raise
+
+
+@dataclass
+class UnionDefinition(JsonSchemaMixin):
+    my_field: Union[str, Dict[str, Any]]
+
+
+def test_union_definition():
+    dct = {"my_field": ["string_a", "string_b"]}
+    with pytest.raises(ValidationError):
+        try:
+            UnionDefinition.from_dict(dct)
+        except ValidationError as exc:
+            assert exc.validator == "oneOf"
+            assert re.search("'type': 'string'", str(exc))
+            assert re.search("'type': 'object'", str(exc))
+            raise