Add testcase for readline-using-libedit on OSX

Lib/test/test_readline.py

+"""
+Very minimal unittests for parts of the readline module.
+
+These tests were added to check that the libedit emulation on OSX and
+the "real" readline have the same interface for history manipulation. That's
+why the tests cover only a small subset of the interface.
+"""
+import unittest
+from test.test_support import run_unittest
+
+import readline
+
+class TestHistoryManipulation (unittest.TestCase):
+    def testHistoryUpdates(self):
+        readline.clear_history()
+
+        readline.add_history("first line")
+        readline.add_history("second line")
+
+        self.assertEqual(readline.get_history_item(0), None)
+        self.assertEqual(readline.get_history_item(1), "first line")
+        self.assertEqual(readline.get_history_item(2), "second line")
+
+        readline.replace_history_item(0, "replaced line")
+        self.assertEqual(readline.get_history_item(0), None)
+        self.assertEqual(readline.get_history_item(1), "replaced line")
+        self.assertEqual(readline.get_history_item(2), "second line")
+
+        self.assertEqual(readline.get_current_history_length(), 2)
+
+        readline.remove_history_item(0)
+        self.assertEqual(readline.get_history_item(0), None)
+        self.assertEqual(readline.get_history_item(1), "second line")
+
+        self.assertEqual(readline.get_current_history_length(), 1)
+
+
+def test_main():
+    run_unittest(TestHistoryManipulation)
+
+if __name__ == "__main__":
+    test_main()