Add simple pexpect test for undo

This acts really strange, I haven't yet figured out why, but I guess it's
a start.

tests/pexpects/undo.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python3
+from pexpect_helper import SpawnedProc
+
+sp = SpawnedProc()
+send, sendline, sleep, expect_prompt, expect_re, expect_str = (
+    sp.send,
+    sp.sendline,
+    sp.sleep,
+    sp.expect_prompt,
+    sp.expect_re,
+    sp.expect_str,
+)
+expect_prompt()
+
+sendline("bind Undo undo; bind Redo redo")
+expect_prompt()
+
+send("echo word")
+expect_str("echo word")
+expect_str("echo word")  # Not sure why we get this twice.
+
+# FIXME why does this only undo one character? It undoes the entire word when run interactively.
+send("Undo")
+expect_str("echo wor")
+
+send("Undo")
+expect_str("echo ")
+
+send("Redo")
+expect_str("echo wor")
+
+# FIXME see above.
+send("Redo")
+expect_str("echo word")