Problem:    Insufficient testing for reading/writing files.
Solution:   Add more tests. (Yegappan Lakshmanan, closes vim/vim#6257)
            Add "ui_delay" to test_override() and use it for the CTRL-O test.
https://github.com/vim/vim/commit/b340baed9f7fc1c19a0742e2214d54982190c15e

Omit test_override().
Reorder test_writefile.vim to match Vim.

Using sleep(10) to wait for typeahead to finish is flaky, especially on
macOS, where legacy/global_spec.lua has failed several times.

Problem:    Some Normal mode commands not fully tested.
Solution:   Add a few more tests. (Yegappan Lakshmanan, closes vim/vim#7073)
https://github.com/vim/vim/commit/d1ad99b65470d3e754f6a0588a6b0dc2214a1eab

Cherry-pick test_registers.vim change from patch 8.2.0644.

Problem:    Mode not updated after CTRL-O CTRL-C in Insert mode.
Solution:   Set redraw_mode and use it. (closes vim/vim#10581)
https://github.com/vim/vim/commit/7a1d32809bb5c1527314000983e75125d79192e0

Problem:    Mode is not cleared when leaving Insert mode with mapped Esc.
Solution:   Clear the mode when redraw_cmdline is set. (closes vim/vim#4269)
https://github.com/vim/vim/commit/4c25bd785aa8b565bf973cbba12ed36b76daaa4f

Problem:    Mode is not cleared when leaving Insert mode.
Solution:   Clear the mode when got_int is set. (Ozaki Kiichi, closes vim/vim#4270)
https://github.com/vim/vim/commit/abc7c7fc5a098374f5543a237e6c9dd918848b34

A timeout of 100 milliseconds is sometimes still too short for macOS.
Change it to 1000 milliseconds.

Problem:    Ex command error cannot contain an argument.
Solution:   Add ex_errmsg() and translate earlier.  Use e_trailing_arg where
            possible.
https://github.com/vim/vim/commit/8930caaa1a283092aca81fdbc3fcf15c7eadb197

Remove duplicate test file 062_tab_pages_spec.lua

Problem:    maparg() does not provide enough information for mapset().
Solution:   Add "lhsraw" and "lhsrawalt" items.  Drop "simplified"
https://github.com/vim/vim/commit/9c65253fe702ea010afec11aa971acd542c35de2

vim-patch:9.0.0127: unused variable

Problem:    Unused variable.
Solution:   Remove the variable. (closes vim/vim#10829)
https://github.com/vim/vim/commit/e95f22f63a1871b91e5508088e5ae4905ce28cd7