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_rpc.py

@@ -0,0 +1,30 @@
+"Test rpc, coverage 20%."
+
+from idlelib import rpc
+import unittest
+
+import marshal
+
+
+class CodePicklerTest(unittest.TestCase):
+
+    def test_pickle_unpickle(self):
+        def f(): return a + b + c
+        func, (cbytes,) = rpc.pickle_code(f.__code__)
+        self.assertIs(func, rpc.unpickle_code)
+        self.assertIn(b'test_rpc.py', cbytes)
+        code = rpc.unpickle_code(cbytes)
+        self.assertEqual(code.co_names, ('a', 'b', 'c'))
+
+    def test_code_pickler(self):
+        self.assertIn(type((lambda:None).__code__),
+                      rpc.CodePickler.dispatch_table)
+
+    def test_dumps(self):
+        def f(): pass
+        # The main test here is that pickling code does not raise.
+        self.assertIn(b'test_rpc.py', rpc.dumps(f.__code__))
+
+
+if __name__ == '__main__':
+    unittest.main(verbosity=2)