Add complete -k group order test

Ensure that multiple `-k` completions intermixed with one or more non-`-k`
completions are produced in the expected order with the order of all completions
in a single `-k` completion respected, non-`-k` completions correctly sorted and
interspersed, and the results of multiple `-k` completions in the
reverse-intuitive order (with chronologically later completions coming before
chronologically earlier `-k` counterparts), as per #9221.

tests/pexpects/complete-group-order.py

@@ -0,0 +1,46 @@
+#!/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,
+)
+
+# This test verifies the overall sort order across multiple `complete -k` completions with identical
+# predicates. We check for legacy "reverse what you'd expect" order, as discussed in #9221.
+
+expect_prompt()
+sendline("function fooc; true; end;")
+expect_prompt()
+
+# A non-`complete -k` completion
+sendline('complete -c fooc -fa "alpha delta bravo"')
+expect_prompt()
+
+# A `complete -k` completion chronologically and alphabetically before the next completion. You'd
+# expect it to come first, but we documented that it will come second.
+sendline('complete -c fooc -fka "golf charlie echo"')
+expect_prompt()
+
+# A `complete -k` completion that is chronologically after and alphabetically after the previous
+# one, so a naive sort would place it after but we want to make sure it comes before.
+sendline('complete -c fooc -fka "india foxtrot hotel"')
+expect_prompt()
+
+# Another non-`complete -k` completion
+sendline('complete -c fooc -fa "kilo juliett lima"')
+expect_prompt()
+
+sendline("set TERM xterm")
+expect_prompt()
+
+# Generate completions
+send('fooc \t')
+
+expect_re("alpha\W+india\W+hotel\W+charlie\W+echo\W+kilo\r\n"
++ "bravo\W+foxtrot\W+golf\W+delta\W+juliett\W+lima")