[3.6] Improve comments in test_idle.py. (GH-7057) (GH-7060)

(cherry picked from commit 2a6d5da)

Author: terryjreedy

Lib/test/test_idle.py

@@ -1,19 +1,23 @@
 import unittest
 from test.support import import_module
 
-# Skip test if _thread or _tkinter wasn't built, if idlelib is missing,
-# or if tcl/tk is not the 8.5+ needed for ttk widgets.
-import_module('threading')  # imported by PyShell, imports _thread
+# For 3.6, skip test_idle if threads are not supported.
+import_module('threading')  # Imported by PyShell, imports _thread.
+
+# Skip test_idle if _tkinter wasn't built, if tkinter is missing,
+# if tcl/tk is not the 8.5+ needed for ttk widgets,
+# or if idlelib is missing (not installed).
 tk = import_module('tkinter')  # imports _tkinter
 if tk.TkVersion < 8.5:
     raise unittest.SkipTest("IDLE requires tk 8.5 or later.")
 idlelib = import_module('idlelib')
 
-# Before test imports, tell IDLE to avoid changing the environment.
+# Before importing and executing more of idlelib,
+# tell IDLE to avoid changing the environment.
 idlelib.testing = True
 
-# unittest.main and test.libregrtest.runtest.runtest_inner
-# call load_tests, when present, to discover tests to run.
+# Unittest.main and test.libregrtest.runtest.runtest_inner
+# call load_tests, when present here, to discover tests to run.
 from idlelib.idle_test import load_tests
 
 if __name__ == '__main__':