Restructure the record of root items in the tree class

tests/test_core/test_core_index.py

@@ -284,6 +284,7 @@ def testCoreIndex_ScanText(nwMinimal, mockGUI):
     aHandle = theProject.newRoot("Archive", nwItemClass.ARCHIVE)
     assert theProject.projTree[aHandle] is not None
     xItem.setParent(aHandle)
+    xItem.setRoot(aHandle)
     assert theIndex.scanText(xHandle, "Hello World!") is False
 
     # Make some usable items

tests/test_core/test_core_tree.py

@@ -224,17 +224,10 @@ def testCoreTree_Methods(mockGUI, mockItems):
     assert theTree.checkType("c000000000001", nwItemType.FILE) is True
 
     # Root item lookup
-    theTree._treeRoots.append("stuff")
     assert theTree.findRoot(nwItemClass.WORLD) is None
     assert theTree.findRoot(nwItemClass.NOVEL) == "a000000000001"
     assert theTree.findRoot(nwItemClass.CHARACTER) == "a000000000004"
 
-    # Find root item of child item
-    assert theTree.getRootItem("b000000000001").itemHandle == "a000000000001"
-    assert theTree.getRootItem("c000000000001").itemHandle == "a000000000001"
-    assert theTree.getRootItem("c000000000002").itemHandle == "a000000000001"
-    assert theTree.getRootItem("stuff") is None
-
     # Get item path
     assert theTree.getItemPath("stuff") == []
     assert theTree.getItemPath("c000000000001") == [