Add validation of view builder during registration

src/dbally/_collection.py

@@ -98,8 +98,15 @@ def build_dogs_df_view():
         if non_default_args and builder is None:
             raise ValueError("Builder function is required for views with non-default arguments")
 
+        builder = builder or view
+
+        # instantiate view to check if the builder is correct
+        view_instance = builder()
+        if not isinstance(view_instance, view):
+            raise ValueError(f"The builder function for view {name} must return an instance of {view.__name__}")
+
         self._views[name] = view
-        self._builders[name] = builder or view
+        self._builders[name] = builder
 
     def get(self, name: str) -> AbstractBaseView:
         """

tests/unit/test_collection.py

@@ -130,7 +130,8 @@ def builder():
     assert len(collection.list()) == 3
 
     view = collection.get("MockViewWithAttributes")
-    mocked_builder.assert_called_once()
+    mocked_builder.assert_called()
+    assert mocked_builder.call_count == 2  # one during registration and one during get
     assert isinstance(view, MockViewWithAttributes)
     assert view.foo == "bar"
 
@@ -157,6 +158,30 @@ def test_error_when_view_with_non_default_args(collection: Collection) -> None:
         assert True
 
 
+def test_error_when_view_builder_with_wrong_return_type(collection: Collection) -> None:
+    """
+    Tests that the add method raises an exception when the view builder returns a wrong type
+    """
+
+    def builder():
+        return MockView1()
+
+    with pytest.raises(ValueError):
+        collection.add(MockViewWithAttributes, builder=builder)
+
+
+def test_error_when_view_incorrect_builder(collection: Collection) -> None:
+    """
+    Tests that the add method raises an exception when the the builder itself raises an exception
+    """
+
+    def builder():
+        raise ValueError("foo")
+
+    with pytest.raises(ValueError):
+        collection.add(MockViewWithAttributes, builder=builder)
+
+
 @pytest.fixture(name="collection_feedback")
 def mock_collection_feedback_loop() -> Collection:
     """