bpo-33855: Still more edits and minimal tests for IDLE (GH-7784)

Part 3 of 3, continuing PR #7689. This covers 14 idlelib modules and their tests,
rpc to zoomheight except for run (already done) and tooltip (being done separately).

Lib/idlelib/idle_test/test_stackviewer.py

@@ -0,0 +1,36 @@
+"Test stackviewer, coverage 19%."
+
+from idlelib import stackviewer
+import unittest
+from test.support import requires
+from tkinter import Tk
+
+
+class Test(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)  # Need for EditorWindow.
+        cls.root.destroy()
+        del cls.root
+
+    def test_init(self):
+        try:
+            zzz
+        except NameError as e:
+            ex = e
+# Test runners suppress setting of sys.last_xyx, which stackviewer needs.
+# Revise stackviewer so following works.
+#        stackviewer.StackBrowser(self.root, ex=exc)
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)