Fixed code style issue.

Author: fzuellich

src/robotide/ui/tree.py

@@ -641,7 +641,7 @@ def _for_all_tests(self, item, func):
                 return
 
             is_item_expanded = self.IsExpanded(item)
-            if is_item_expanded is False:
+            if not is_item_expanded:
                 self.Expand(item)
             if self._is_test_node(item):
                 func(item)
@@ -651,7 +651,7 @@ def _for_all_tests(self, item, func):
         for child in item.GetChildren():
             self._for_all_tests(child, func)
 
-        if is_item_expanded is False:
+        if not is_item_expanded:
             self.Collapse(item)
 
     def _for_all_drawn_tests(self, item, func):