Store toolbox in test_case._toolbox

Apparently accessing double-underscore variables in threads leads
to name-mangling issues, so effectively updating test_case.__toolbox
wouldn't be reflected outside of the watcher thread.
We previously used self.app.toolbox which circumenvented
this issue.
It is possible that `check_tool_errors` / `check_no_tool_errors`
were accessing the old toolbox, unless the watching thread happened
to fire between function definition and assert, and that's probably
why increasing the number of trials had no effect.

test/unit/tools/test_toolbox.py

@@ -51,11 +51,9 @@ def assert_integerated_tool_panel(self, exists=True):
 
     @property
     def toolbox(self):
-        if self.__toolbox is None:
-            self.__toolbox = SimplifiedToolBox(self)
-            # wire app with this new toolbox
-            self.app.toolbox = self.__toolbox
-        return self.__toolbox
+        if self._toolbox is None:
+            self.app.toolbox = self._toolbox = SimplifiedToolBox(self)
+        return self._toolbox
 
     def setUp(self):
         self.reindexed = False
@@ -67,7 +65,7 @@ def setUp(self):
         itp_config = os.path.join(self.test_directory, "integrated_tool_panel.xml")
         self.app.config.integrated_tool_panel_config = itp_config
         self.app.watchers = ConfigWatchers(self.app)
-        self.__toolbox = None
+        self._toolbox = None
         self.config_files = []
 
     def _repo_install(self, changeset, config_filename=None):
@@ -197,7 +195,7 @@ def test_tool_reload_when_macro_is_altered(self):
             macro_out.write(SIMPLE_MACRO.substitute(tool_version="3.0"))
 
         def check_tool_macro():
-            tool = self.app.toolbox.get_tool("tool_with_macro")
+            tool = self.toolbox.get_tool("tool_with_macro")
             assert tool.version == "3.0"
 
         self._try_until_no_errors(check_tool_macro)
@@ -216,7 +214,7 @@ def test_tool_reload_for_broken_tool(self):
             out.write('certainly not a valid tool')
 
         def check_tool_errors():
-            tool = self.app.toolbox.get_tool("test_tool")
+            tool = self.toolbox.get_tool("test_tool")
             assert tool is not None
             assert tool.version == "1.0"
             assert tool.tool_errors == 'Current on-disk tool is not valid'
@@ -227,7 +225,7 @@ def check_tool_errors():
         self._init_tool(filename="simple_tool.xml", version="2.0")
 
         def check_no_tool_errors():
-            tool = self.app.toolbox.get_tool("test_tool")
+            tool = self.toolbox.get_tool("test_tool")
             assert tool is not None
             assert tool.version == "2.0"
             assert tool.tool_errors is None
@@ -562,4 +560,4 @@ def handle_panel_update(self, section_dict):
 
 def reload_callback(test_case):
     test_case.app.tool_cache.cleanup()
-    test_case.__toolbox = test_case.app.toolbox = SimplifiedToolBox(test_case)
+    test_case._toolbox = test_case.app.toolbox = SimplifiedToolBox(test_case)