[3.6] bpo-30917: IDLE: Add config.IdleConf unittests (GH-2691) (#2753)

Patch by Louie Lu.
(cherry picked from commit f776eb0f)
(includes diffs of  ed014f7e and 9f9192af)
* fix config reset from pr 2754

* Fix test_get_font (from pr 2769)

Lib/idlelib/config.py

@@ -30,6 +30,7 @@ import os
 import sys
 
 from tkinter.font import Font
+import idlelib
 
 class InvalidConfigType(Exception): pass
 class InvalidConfigSet(Exception): pass
@@ -159,14 +160,15 @@ class IdleConf:
         for config_type in self.config_types:
         (user home dir)/.idlerc/config-{config-type}.cfg
     """
-    def __init__(self):
+    def __init__(self, _utest=False):
         self.config_types = ('main', 'highlight', 'keys', 'extensions')
         self.defaultCfg = {}
         self.userCfg = {}
         self.cfg = {}  # TODO use to select userCfg vs defaultCfg
-        self.CreateConfigHandlers()
-        self.LoadCfgFiles()
 
+        if not _utest:
+            self.CreateConfigHandlers()
+            self.LoadCfgFiles()
 
     def CreateConfigHandlers(self):
         "Populate default and user config parser dictionaries."
@@ -215,7 +217,8 @@ class IdleConf:
             except OSError:
                 warn = ('\n Warning: unable to create user config directory\n' +
                         userDir + '\n Check path and permissions.\n Exiting!\n')
-                print(warn, file=sys.stderr)
+                if not idlelib.testing:
+                    print(warn, file=sys.stderr)
                 raise SystemExit
         # TODO continue without userDIr instead of exit
         return userDir
@@ -463,16 +466,7 @@ class IdleConf:
 
     def RemoveKeyBindNames(self, extnNameList):
         "Return extnNameList with keybinding section names removed."
-        # TODO Easier to return filtered copy with list comp
-        names = extnNameList
-        kbNameIndicies = []
-        for name in names:
-            if name.endswith(('_bindings', '_cfgBindings')):
-                kbNameIndicies.append(names.index(name))
-        kbNameIndicies.sort(reverse=True)
-        for index in kbNameIndicies: #delete each keybinding section name
-            del(names[index])
-        return names
+        return [n for n in extnNameList if not n.endswith(('_bindings', '_cfgBindings'))]
 
     def GetExtnNameForEvent(self, virtualEvent):
         """Return the name of the extension binding virtualEvent, or None.

Misc/NEWS.d/next/IDLE/2017-07-17-23-35-57.bpo-30917.hSiuuO.rst

+Add tests for idlelib.config.IdleConf.
+Increase coverage from 46% to 96%.
+Patch by Louie Lu.