patch 8.2.0049: command line completion not fully tested

Problem:    Command line completion not fully tested.
Solution:   Add more test cases.  Make help sorting stable. (Dominique Pelle,
            closes #5402)
diff --git a/src/testdir/test_menu.vim b/src/testdir/test_menu.vim
index 0d6b78e..04d45d6 100644
--- a/src/testdir/test_menu.vim
+++ b/src/testdir/test_menu.vim
@@ -45,6 +45,10 @@
   imenu 2 Test.FooBar :let g:did_menu = 'insert'<CR>
   cmenu 2 Test.FooBar :let g:did_menu = 'cmdline'<CR>
   emenu n Test.FooBar
+
+  call feedkeys(":menu Test.FooB\<C-A>\<C-B>\"\<CR>", 'tx')
+  call assert_equal('"menu Test.FooBar', @:)
+
   call assert_equal('normal', g:did_menu)
   emenu v Test.FooBar
   call assert_equal('visual', g:did_menu)