fixed up 'xor' arg functionality

Author: tclose

pydra/engine/specs.py

@@ -511,8 +511,8 @@ def _rule_violations(self) -> list[str]:
                     )
                 elif not are_set:
                     errors.append(
-                        f"At least one of the mutually exclusive fields ({', '.join(field.xor)}) "
-                        f"should be set"
+                        "At least one of the mutually exclusive fields should be set: "
+                        + ", ".join(f"{n}={v!r}" for n, v in mutually_exclusive.items())
                     )
 
             # Raise error if any required field is unset.

pydra/engine/tests/test_shelltask_inputspec.py

@@ -1496,7 +1496,7 @@ def test_task_inputs_mandatory_with_xOR_zero_mandatory_raises_error():
     simple_xor = SimpleXor()
     simple_xor.input_2 = False
     with pytest.raises(
-        ValueError, match="At least one of the mutually exclusive fields"
+        ValueError, match="At least one of the mutually exclusive fields should be set:"
     ):
         simple_xor._check_rules()