add tests for non-injectable items in OverrideRule

tests/test_injection.py

@@ -332,6 +332,77 @@ def callback(response: DummyResponse, price_po: PricePO, rate_po: EurDollarRate)
             assert item == {"price": 22, "currency": "€"}
 
 
+class InjectableItem(Injectable):
+    is_injectable = True
+
+
+class NonInjectableItem:
+    is_injectable = False
+
+
+class TestInjectableProperties:
+    """This looks at the consequences when an item/po does not inherit from
+    ``web_poet.Injectable``.
+    """
+
+    pattern = Patterns(["example.com"])
+
+    @staticmethod
+    def get_deps(overrides, callback, providers):
+        registry = OverridesRegistry(overrides)
+        injector = get_injector_for_testing(providers, overrides_registry=registry)
+        response = get_response_for_testing(callback)
+        kwargs = yield from injector.build_callback_dependencies(
+            response.request, response)
+        kwargs_types = {key: type(value) for key, value in kwargs.items()}
+        return kwargs_types
+
+    @inlineCallbacks
+    def test_non_injectable_source(self, providers):
+        """This ensures that overriding an object from ``instead_of`` which is
+        not injectable still works.
+        """
+        overrides = [
+            OverrideRule(self.pattern, use=InjectableItem, instead_of=NonInjectableItem)
+        ]
+
+        def callback(response: DummyResponse, item: NonInjectableItem):
+            pass
+
+        kwargs_types = yield from self.get_deps(overrides, callback, providers)
+        assert kwargs_types == {"item": InjectableItem}
+
+    @inlineCallbacks
+    def test_non_injectable_replacement(self, providers):
+        """By its nature, the replacement asked using the ``use`` param must
+        be an injectable so that the override component would work.
+        """
+        overrides = [
+            OverrideRule(self.pattern, use=NonInjectableItem, instead_of=InjectableItem)
+        ]
+
+        def callback(response: DummyResponse, item: InjectableItem):
+            pass
+
+        kwargs_types = yield from self.get_deps(overrides, callback, providers)
+        assert kwargs_types == {}
+
+    @inlineCallbacks
+    def test_non_injectable_source_and_replacement(self, providers):
+        """Having both of ``instead_of`` and ``use`` not being Injectables won't
+        work at all.
+        """
+        overrides = [
+            OverrideRule(self.pattern, use=NonInjectableItem, instead_of=NonInjectableItem)
+        ]
+
+        def callback(response: DummyResponse, item: NonInjectableItem):
+            pass
+
+        kwargs_types = yield from self.get_deps(overrides, callback, providers)
+        assert kwargs_types == {}
+
+
 def test_load_provider_classes():
     provider_as_string = f"{ResponseDataProvider.__module__}.{ResponseDataProvider.__name__}"
     injector = get_injector_for_testing({provider_as_string: 2, ResponseDataProvider: 1})