bpo-33855: Minimally test all IDLE modules. (GH-7689)

Create a template for minimally testing a tkinter-using module by importing it and instantiating its class(es).  Add a test file for all non-startup IDLE modules.  Edit existing files and update coverage.  This is part 1 of 3, covering the 21 autocomplete to help modules and touching 33 idlelib files.

Lib/idlelib/idle_test/test_filelist.py

@@ -0,0 +1,33 @@
+"Test filelist, coverage 19%."
+
+from idlelib import filelist
+import unittest
+from test.support import requires
+from tkinter import Tk
+
+class FileListTest(unittest.TestCase):
+
+    @classmethod
+    def setUpClass(cls):
+        requires('gui')
+        cls.root = Tk()
+        cls.root.withdraw()
+
+    @classmethod
+    def tearDownClass(cls):
+        cls.root.update_idletasks()
+        for id in cls.root.tk.call('after', 'info'):
+            cls.root.after_cancel(id)
+        cls.root.destroy()
+        del cls.root
+
+    def test_new_empty(self):
+        flist = filelist.FileList(self.root)
+        self.assertEqual(flist.root, self.root)
+        e = flist.new()
+        self.assertEqual(type(e), flist.EditorWindow)
+        e._close()
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)