Problem:    Undo earlier test sometimes fails on MS-Windows.
Solution:   Use another file name.
https://github.com/vim/vim/commit/cce293f87beb57a75ff738fade7fafadbc4a78a9

Problem:    Various code not covered by tests.
Solution:   Add a few more test. (Yegappan Lakshmanan, closes vim/vim#7995)
https://github.com/vim/vim/commit/1f448d906b3c516e5864dc5bae3ddbf3664ee649

Cherry-pick some test_edit.vim changes from patches 8.2.{1022,1432}.
Reorder test_undo.vim to match upstream.

Problem:    Character input not fully tested.
Solution:   Add more tests. (Yegappan Lakshmanan, closes vim/vim#7963)
https://github.com/vim/vim/commit/f4fcedc59d4cc5ae6b5270a933e8377030283c1c

Cherry-pick related changes from patches 8.2.{0433,0866}.

Problem:    Insufficient code coverage for ex_docmd.c functions.
Solution:   Add more tests. (Yegappan Lakshmanan, closes vim/vim#5618)
https://github.com/vim/vim/commit/9f6277bdde97b7767ded43a0b5a2023eb601b3b7

Cherry-pick Test_window_only() from patch 8.2.0203.
Cherry-pick a memory leak fix from patch 8.2.0399.

Problem:    When :edit reuses the current buffer the alternate file is set to
            the same buffer.
Solution:   Only set the alternate file when not reusing the buffer.
            (closes vim/vim#8783)
https://github.com/vim/vim/commit/b8bd2e6ebab03baf2672067067a599df69a278c0

Cherry-pick Test_cmdline_expand_special() from patches 8.2.{0243,2873}.
Move Test_cmd_backtick() to the right place.

Problem:    '[ and '] marks may be wrong after undo.
Solution:   Adjust the '[ and '] marks if needed. (closes vim/vim#10407, closes vim/vim#1281)
https://github.com/vim/vim/commit/82444cefa3fef87624a078ea86a72af7ef4ef42e

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
https://github.com/vim/vim/commit/f92e58cadb03156879e9bdbf6341bf662d9c87cc

Cherry-pick s:normalize_fname for tolower test from v8.1.0894 and v8.1.1417 (even though it is
unused for now).

Fix header for win_id2tabwin in eval.txt.

Some skipped tests have custom error messages.
Use ":CheckFunction" command for standard error message
on missing function.

Problem:    Undo file not found when using ":args" or ":next".
Solution:   Handle like editing another file. (closes vim/vim#7072)
https://github.com/vim/vim/commit/55b419b871dd35f5b05dd2aed65f14461b493ba9