fix(ModelItem): better error message on bogus constructor param

Author: yt-ms

CHANGELOG.rst

@@ -4,6 +4,7 @@ History
 
 Next Release
 ------------
+* Fix: Better error on bad ModelItem constructor argument (#50)
 
 0.2.1 (2020-11-27)
 ------------------

src/structurizr/model/model_item.py

@@ -84,7 +84,17 @@ def __init__(
         **kwargs,
     ):
         """Initialise a ModelItem instance."""
-        super().__init__(**kwargs)
+        if len(kwargs) > 0:
+            type_name = type(self).__name__
+            args = [f"'{key}'" for key in kwargs.keys()]
+            if len(args) == 1:
+                raise TypeError(f"{type_name}.__init__() got an unexpected "
+                                f"keyword argument {args[0]}")
+            else:
+                raise TypeError(f"{type_name}.__init__() got unexpected "
+                                f"keyword arguments {', '.join(args)}")
+
+        super().__init__()
         self.id = id
         self.tags = OrderedSet(tags)
         self.properties = dict(properties)

tests/unit/model/test_model_item.py

@@ -45,6 +45,25 @@ def test_model_item_init(attributes):
         assert getattr(model_item, attr) == expected
 
 
+def test_handling_of_bogus_init_params():
+    """
+    Test for sensible error message if wrong param passed.
+
+    See https://github.com/Midnighter/structurizr-python/issues/50.
+    """
+    with pytest.raises(
+        TypeError, match=r"ConcreteModelItem.__init__\(\) got an unexpected "
+                         r"keyword argument 'foo'"
+    ):
+        ConcreteModelItem(foo=7)
+    with pytest.raises(
+        TypeError,
+        match=r"ConcreteModelItem.__init__\(\) got unexpected keyword "
+              r"arguments 'foo', 'bar'",
+    ):
+        ConcreteModelItem(foo=7, bar=17)
+
+
 def test_default_element_tags_order(empty_model: Model):
     """
     Test that the default tags get added in the right order.