Better error messages for unknown initialization keyword arguments

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/abstract_base.py

@@ -25,6 +25,28 @@
 class AbstractBase(ABC):
     """Define common business logic through an abstract base class."""
 
+    def __init__(self, **kwargs):
+        """
+        Initialize an abstract base class.
+
+        The AbstractBase class is designed to be the singular root of the entire class
+        hierarchy, similar to `object`, and acts as a guard against unknown keyword
+        arguments. Any keyword arguments not consumed in the hierarchy above cause a
+        `TypeError`.
+
+        """
+        if kwargs:
+            phrase = (
+                "unexpected keyword arguments"
+                if len(kwargs) > 1
+                else "an unexpected keyword argument"
+            )
+            message = "\n    ".join(f"{key}={value}" for key, value in kwargs.items())
+            raise TypeError(
+                f"{type(self).__name__}.__init__() got {phrase}:\n    {message}"
+            )
+        super().__init__()
+
     def __hash__(self) -> int:
         """Return an integer that represents a unique hash value for this instance."""
         return id(self)

tests/unit/model/test_model_item.py

@@ -45,6 +45,36 @@ def test_model_item_init(attributes):
         assert getattr(model_item, attr) == expected
 
 
+@pytest.mark.parametrize(
+    "kwargs",
+    [
+        pytest.param(
+            {"foo": 7},
+            marks=pytest.mark.raises(
+                exception=TypeError,
+                message="ConcreteModelItem.__init__() got an unexpected keyword "
+                "argument:\n    foo=7",
+            ),
+        ),
+        pytest.param(
+            {"foo": 7, "bar": 17},
+            marks=pytest.mark.raises(
+                exception=TypeError,
+                message="ConcreteModelItem.__init__() got unexpected keyword "
+                "arguments:\n    foo=7\n    bar=17",
+            ),
+        ),
+    ],
+)
+def test_handle_unknown_argument(kwargs: dict):
+    """
+    Test for a sensible error message when unknown keyword arguments are passed.
+
+    See https://github.com/Midnighter/structurizr-python/issues/50.
+    """
+    ConcreteModelItem(**kwargs)
+
+
 def test_default_element_tags_order(empty_model: Model):
     """
     Test that the default tags get added in the right order.