Add test for gcodeListDecorator

It's super simple, but hey, it's also easy to write.

cura/Scene/GCodeListDecorator.py

@@ -10,7 +10,7 @@ class GCodeListDecorator(SceneNodeDecorator):
     def getGCodeList(self) -> List[str]:
         return self._gcode_list
 
-    def setGCodeList(self, list: List[str]):
+    def setGCodeList(self, list: List[str]) -> None:
         self._gcode_list = list
 
     def __deepcopy__(self, memo) -> "GCodeListDecorator":

tests/TestGCodeListDecorator.py

@@ -0,0 +1,16 @@
+from cura.Scene.GCodeListDecorator import GCodeListDecorator
+
+
+def test_setAndGetList():
+    decorator = GCodeListDecorator()
+
+    decorator.setGCodeList(["Test"])
+    assert decorator.getGCodeList() == ["Test"]
+
+
+def test_copyGCodeDecorator():
+    decorator = GCodeListDecorator()
+    decorator.setGCodeList(["Test"])
+    import copy
+    copied_decorator = copy.deepcopy(decorator)
+    assert decorator.getGCodeList() == copied_decorator.getGCodeList()