Problem:    Failure to compile a pattern not tested much.
Solution:   Add tests where a pattern fails to compile. (Yegappan Lakshmanan,
            closes vim/vim#7004)

https://github.com/vim/vim/commit/531be47ac5522807b265c6287021a01c9b895ac9

Problem:    assert_fails() checks the last error message.
Solution:   Check the first error, it is more relevant.  Fix all the tests
            that rely on the old behavior.

https://github.com/vim/vim/commit/9b7bf9e98f06ece595fed7a3ff53ecce89797a53

Skip test_listener.vim, test_textprop.vim, test_viminfo.vim.
Skip test_python2.vim: affected line fails and hasn't been ported.
Skip test_python3.vim: affected lines fail and haven't been ported.
Skip CHECK_LIST_MATERIALIZE.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

Problem:    Not enough tests for buffer writing.
Solution:   Add more tests. Use CheckRunVimInTerminal in more places.
            (Yegappan Lakshmanan, closes vim/vim#6167)

https://github.com/vim/vim/commit/494e9069cb32620f7688a7cb128a3feff827639e

Problem:    Various functions not properly tested.
Solution:   Add more tests, especially for failures. (Yegappan Lakshmanan,
            closes vim/vim#5843)

https://github.com/vim/vim/commit/0e05de46226eb4e5ea580beefa71831f92d613d3

Cherry-pick test changes from patch 8.2.0427 and skip Test_has().
Cherry-pick Test_complete_wildmenu() change from patch 8.2.4339.

Problem:    Using \z() with \z1 not tested for syntax highlighting.
Solution:   Add a test. (Dominique Pellé, closes vim/vim#9365)

https://github.com/vim/vim/commit/354b23a9f87fd8c5aec457d88320a0a5bce4b985

Co-authored-by: Dominique Pelle <dominique.pelle@gmail.com>

Problem:    Various code lines not covered by tests.
Solution:   Add test cases. (Dominique Pellé, closes vim/vim#8178)

https://github.com/vim/vim/commit/6d37e8e3baafba460bd2d051170d213c1ba9a523

Co-authored-by: Dominique Pelle <dominique.pelle@gmail.com>

Problem:    Several syntax HL errors not checked.
Solution:   Add tests. (Yegappan Lakshmanan, closes vim/vim#5954)

https://github.com/vim/vim/commit/fbf2122cf920a89274ffbefaaeb6c5eeacf5187b

Problem:    Various errors not tested.
Solution:   Add tests. (Yegappan Lakshmanan, closes vim/vim#5895)

https://github.com/vim/vim/commit/476a613135bdc94e61c1dce8a9cbb4ab0b6dc2d1

Need to remove "F" flag from 'shortmess' as early as possible.

Problem:    Tests use hand coded feature and option checks.
Solution:   Use the commands from check.vim in more tests.

https://github.com/vim/vim/commit/8c5a278fc508da6dfe50e69b6ee734451aa4eafb

Omit Test_wincolor(): there are later patches that touch that function.
Omit test_memory_usage.vim: a Lua test is used for that file.
Cherry-pick Test_issue_3969() from patch 8.1.0969.

Co-authored-by: Bram Moolenaar <Bram@vim.org>

Problem:    Some tests are still old style.
Solution:   Convert to new style tests. (Yegappan Lakshmanan, closes vim/vim#5957)

https://github.com/vim/vim/commit/08f4157c5cabc55bcb22f04dd7c717aba40caa34

Fix missing error message when sort() compare function fails.
Cherry-pick a line in test_utf8.vim from patch 8.2.0448.
Cherry-pick builtin_function() change from patch 8.2.0595.