fix error reporting on unknown attribute inquiry (#1393)

PySDM/attributes/impl/attribute_registry.py

@@ -54,7 +54,7 @@ def get_attribute_class(name, dynamics=None, formulae=None):
     if name not in _ATTRIBUTES_REGISTRY:
         raise ValueError(
             f"Unknown attribute name: {name};"
-            " valid names: {', '.join(sorted(_ATTRIBUTES_REGISTRY))}"
+            f" valid names: {', '.join(sorted(_ATTRIBUTES_REGISTRY))}"
         )
     for cls, func in _ATTRIBUTES_REGISTRY[name].items():
         if func(dynamics, formulae):

tests/unit_tests/attributes/test_impl_attribute_registry.py

@@ -20,7 +20,7 @@ def test_get_attribute_class_ok():
     def test_get_attribute_class_fail():
         """checks if inquiring for an invalid attribute name raises an exception"""
         with pytest.raises(ValueError):
-            assert get_attribute_class("lorem ipsum")
+            get_attribute_class("lorem ipsum")
 
     @staticmethod
     def test_get_attribute_class_variant_fail():
@@ -31,7 +31,14 @@ class Umaminess:  # pylint: disable=unused-variable,too-few-public-methods
             """Dummy class"""
 
         with pytest.raises(AssertionError):
-            assert get_attribute_class("umaminess")
+            get_attribute_class("umaminess")
+
+    @staticmethod
+    def test_get_attribute_class_error_message_hints():
+        """check if error message thrown on unknown attribute error contains list of valid names"""
+        with pytest.raises(ValueError) as excinfo:
+            get_attribute_class("XXX")
+        assert "multiplicity" in str(excinfo.value)
 
     @staticmethod
     def test_register_attribute_fail_on_repeated_name():