Add test for registring containers

This test tests adding container stacks and seeing if they convert well.

Contributes to issue CURA-3427.

tests/Settings/TestCuraContainerRegistry.py

@@ -11,6 +11,7 @@ from cura.Settings.CuraContainerRegistry import CuraContainerRegistry #The class
 from cura.Settings.ExtruderStack import ExtruderStack #Testing for returning the correct types of stacks.
 from cura.Settings.GlobalStack import GlobalStack #Testing for returning the correct types of stacks.
 from UM.Resources import Resources #Mocking some functions of this.
+import UM.Settings.InstanceContainer #Creating instance containers to register.
 import UM.Settings.ContainerRegistry #Making empty container stacks.
 import UM.Settings.ContainerStack #Setting the container registry here properly.
 from UM.Settings.DefinitionContainer import DefinitionContainer
@@ -18,7 +19,10 @@ from UM.Settings.DefinitionContainer import DefinitionContainer
 ##  Gives a fresh CuraContainerRegistry instance.
 @pytest.fixture()
 def container_registry():
-    return CuraContainerRegistry()
+    registry = CuraContainerRegistry()
+    UM.Settings.InstanceContainer.setContainerRegistry(registry)
+    UM.Settings.ContainerStack.setContainerRegistry(registry)
+    return registry
 
 def teardown():
     #If the temporary file for the legacy file rename test still exists, remove it.
@@ -26,6 +30,23 @@ def teardown():
     if os.path.isfile(temporary_file):
         os.remove(temporary_file)
 
+##  Tests whether the addContainer function properly converts ContainerStacks.
+def test_addContainerExtruderStack(container_registry):
+    definition = DefinitionContainer(container_id = "Test Definition") #Need some definition first to be able to register stacks.
+    container_registry.addContainer(definition)
+
+    container_stack = UM.Settings.ContainerStack.ContainerStack(stack_id = "Test Container Stack") #A container we're going to convert.
+    container_stack.addMetaDataEntry("type", "extruder_train") #This is now an extruder train.
+    container_stack.insertContainer(0, definition) #Add a definition to it so it doesn't complain.
+
+    mock_super_add_container = unittest.mock.MagicMock()
+    with unittest.mock.patch("UM.Settings.ContainerRegistry.ContainerRegistry.addContainer", mock_super_add_container):
+        container_registry.addContainer(container_stack)
+
+    assert len(mock_super_add_container.call_args_list) == 1 #Called only once.
+    assert len(mock_super_add_container.call_args_list[0][0]) == 1 #Called with one parameter.
+    assert type(mock_super_add_container.call_args_list[0][0][0]) == ExtruderStack
+
 ##  Tests whether loading gives objects of the correct type.
 @pytest.mark.parametrize("filename,                  output_class", [
                         ("ExtruderLegacy.stack.cfg", ExtruderStack),