Split out updating the machine size properties so it can be tested easily

cura/BuildVolume.py

@@ -651,14 +651,10 @@ class BuildVolume(SceneNode):
                     self._height = self._global_container_stack.getProperty("machine_height", "value")
                     self._build_volume_message.hide()
                 update_disallowed_areas = True
-                rebuild_me = True
 
             # sometimes the machine size or shape settings are adjusted on the active machine, we should reflect this
             if setting_key in self._machine_settings:
-                self._height = self._global_container_stack.getProperty("machine_height", "value")
-                self._width = self._global_container_stack.getProperty("machine_width", "value")
-                self._depth = self._global_container_stack.getProperty("machine_depth", "value")
-                self._shape = self._global_container_stack.getProperty("machine_shape", "value")
+                self._updateMachineSizeProperties()
                 update_extra_z_clearance = True
                 update_disallowed_areas = True
 
@@ -703,6 +699,14 @@ class BuildVolume(SceneNode):
     def hasErrors(self) -> bool:
         return self._has_errors
 
+    def _updateMachineSizeProperties(self) -> None:
+        if not self._global_container_stack:
+            return
+        self._height = self._global_container_stack.getProperty("machine_height", "value")
+        self._width = self._global_container_stack.getProperty("machine_width", "value")
+        self._depth = self._global_container_stack.getProperty("machine_depth", "value")
+        self._shape = self._global_container_stack.getProperty("machine_shape", "value")
+
     ##  Calls _updateDisallowedAreas and makes sure the changes appear in the
     #   scene.
     #

tests/TestBuildVolume.py

@@ -201,3 +201,32 @@ class TestRebuild:
         build_volume.rebuild()
         assert build_volume.getMeshData() is None
 
+
+
+class TestUpdateMachineSizeProperties:
+    setting_property_dict = {"machine_width": {"value": 50},
+                             "machine_depth": {"value": 100},
+                             "machine_height": {"value": 200},
+                             "machine_shape": {"value": "DERP!"}}
+
+    def getPropertySideEffect(*args, **kwargs):
+        properties = TestUpdateMachineSizeProperties.setting_property_dict.get(args[1])
+        if properties:
+            return properties.get(args[2])
+
+    def test_noGlobalStack(self, build_volume: BuildVolume):
+        build_volume._updateMachineSizeProperties()
+        assert build_volume._width == 0
+        assert build_volume._height == 0
+        assert build_volume._depth == 0
+        assert build_volume._shape == ""
+
+    def test_happy(self, build_volume: BuildVolume):
+        mocked_global_stack = MagicMock(name="mocked_global_stack")
+        mocked_global_stack.getProperty = MagicMock(side_effect=self.getPropertySideEffect)
+        build_volume._global_container_stack = mocked_global_stack
+        build_volume._updateMachineSizeProperties()
+        assert build_volume._width == 50
+        assert build_volume._height == 200
+        assert build_volume._depth == 100
+        assert build_volume._shape == "DERP!"