Add Container provider tests

tests/unit/providers/test_traversal_py3.py

@@ -1,6 +1,6 @@
 import unittest
 
-from dependency_injector import providers
+from dependency_injector import containers, providers
 
 
 class TraverseTests(unittest.TestCase):
@@ -625,3 +625,49 @@ class ResourceTests(unittest.TestCase):
 
         self.assertEqual(len(all_providers), 1)
         self.assertIn(provider1, all_providers)
+
+
+class ContainerTests(unittest.TestCase):
+
+    def test_traverse(self):
+        class Container(containers.DeclarativeContainer):
+            provider1 = providers.Callable(list)
+            provider2 = providers.Callable(dict)
+
+        provider = providers.Container(Container)
+
+        all_providers = list(provider.traverse())
+
+        self.assertEqual(len(all_providers), 2)
+        self.assertEqual(
+            {provider.provides for provider in all_providers},
+            {list,  dict},
+        )
+
+    def test_traverse_overridden(self):
+        class Container1(containers.DeclarativeContainer):
+            provider1 = providers.Callable(list)
+            provider2 = providers.Callable(dict)
+
+        class Container2(containers.DeclarativeContainer):
+            provider1 = providers.Callable(tuple)
+            provider2 = providers.Callable(str)
+
+        container2 = Container2()
+
+        provider = providers.Container(Container1)
+        provider.override(container2)
+
+        all_providers = list(provider.traverse())
+
+        self.assertEqual(len(all_providers), 5)
+        self.assertEqual(
+            {
+                provider.provides
+                for provider in all_providers
+                if isinstance(provider, providers.Callable)
+            },
+            {list, dict, tuple, str},
+        )
+        self.assertIn(provider.last_overriding, all_providers)
+        self.assertIs(provider.last_overriding(), container2)