Add tests for Dependency provider

src/dependency_injector/containers.pyx

@@ -311,7 +311,10 @@ class DynamicContainer(Container):
         if self.parent:
             return self.parent.parent_name
 
-        return self.declarative_parent.__name__
+        if self.declarative_parent:
+            return self.declarative_parent.__name__
+
+        return None
 
     def assign_parent(self, parent):
         """Assign parent."""

src/dependency_injector/providers.pyx

@@ -735,7 +735,13 @@ cdef class Dependency(Provider):
         """Return parent name."""
         if not self.__parent:
             return None
-        return f'{self.__parent.parent_name}.{self.__parent.resolve_provider_name(self)}'
+
+        name = ''
+        if self.__parent.parent_name:
+            name += f'{self.__parent.parent_name}.'
+        name += f'{self.__parent.resolve_provider_name(self)}'
+
+        return name
 
     def assign_parent(self, parent):
         """Assign parent."""

tests/unit/providers/test_base_py2_py3.py

@@ -360,8 +360,118 @@ class DependencyTests(unittest.TestCase):
         self.provider.provided_by(providers.Factory(dict))
         self.assertRaises(errors.Error, self.provider)
 
-    def test_call_not_overridden(self):
-        self.assertRaises(errors.Error, self.provider)
+    def test_call_undefined(self):
+        with self.assertRaises(errors.Error) as context:
+            self.provider()
+        self.assertEqual(str(context.exception), 'Dependency is not defined')
+
+    def test_call_undefined_error_message_with_container_instance_parent(self):
+        class UserService:
+            def __init__(self, database):
+                self.database = database
+
+        class Container(containers.DeclarativeContainer):
+            database = providers.Dependency()
+
+            user_service = providers.Factory(
+                UserService,
+                database=database,  # <---- missing dependency
+            )
+
+        container = Container()
+
+        with self.assertRaises(errors.Error) as context:
+            container.user_service()
+
+        self.assertEqual(str(context.exception), 'Dependency "Container.database" is not defined')
+
+    def test_call_undefined_error_message_with_container_provider_parent_deep(self):
+        class Database:
+            pass
+
+        class UserService:
+            def __init__(self, db):
+                self.db = db
+
+        class Gateways(containers.DeclarativeContainer):
+            database_client = providers.Singleton(Database)
+
+        class Services(containers.DeclarativeContainer):
+            gateways = providers.DependenciesContainer()
+
+            user = providers.Factory(
+                UserService,
+                db=gateways.database_client,
+            )
+
+        class Container(containers.DeclarativeContainer):
+            gateways = providers.Container(Gateways)
+
+            services = providers.Container(
+                Services,
+                # gateways=gateways,  # <---- missing dependency
+            )
+
+        container = Container()
+
+        with self.assertRaises(errors.Error) as context:
+            container.services().user()
+
+        self.assertEqual(
+            str(context.exception),
+            'Dependency "Container.services.gateways.database_client" is not defined',
+        )
+
+    def test_call_undefined_error_message_with_dependenciescontainer_provider_parent(self):
+        class UserService:
+            def __init__(self, db):
+                self.db = db
+
+        class Services(containers.DeclarativeContainer):
+            gateways = providers.DependenciesContainer()
+
+            user = providers.Factory(
+                UserService,
+                db=gateways.database_client,  # <---- missing dependency
+            )
+
+        services = Services()
+
+        with self.assertRaises(errors.Error) as context:
+            services.user()
+
+        self.assertEqual(
+            str(context.exception),
+            'Dependency "Services.gateways.database_client" is not defined',
+        )
+
+    def test_assign_parent(self):
+        parent = providers.DependenciesContainer()
+        provider = providers.Dependency()
+
+        provider.assign_parent(parent)
+
+        self.assertIs(provider.parent, parent)
+
+    def test_parent_name(self):
+        container = containers.DynamicContainer()
+        provider = providers.Dependency()
+        container.name = provider
+        self.assertEqual(provider.parent_name, 'name')
+
+    def test_deepcopy_parent(self):
+        container = containers.DynamicContainer()
+        provider = providers.Dependency()
+        container.name = provider
+
+        copied = providers.deepcopy(container)
+
+        self.assertIs(container.name.parent, container)
+        self.assertIs(copied.name.parent, copied)
+
+        self.assertIsNot(container, copied)
+        self.assertIsNot(container.name, copied.name)
+        self.assertIsNot(container.name.parent, copied.name.parent)
 
     def test_deepcopy(self):
         provider = providers.Dependency(int)