Improve comments in test_idle.py. (GH-7057)

Lib/test/test_idle.py

@@ -1,18 +1,20 @@
 import unittest
 from test.support import import_module
 
-# Skip test if _tkinter wasn't built, if idlelib is missing,
-# or if tcl/tk is not the 8.5+ needed for ttk widgets.
-tk = import_module('tkinter')  # imports _tkinter
+# 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')  # Also 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__':