The new oldtest directory is in test/old/testdir. The reason for this is
that many tests have hardcoded the parent directory name to be
'testdir'.

Problem:    Several errors are not tested for.
Solution:   Add tests. (Yegappan Lakshmanan, closes vim/vim#5892)
https://github.com/vim/vim/commit/ee4e0c1e9a81cb5d96e0060203a9033c2f28588e

Omit Test_range() change: reverted in patch 8.2.0615.
Cherry-pick Test_z_no_space_before_xxx() from patch 8.2.0195.
Cherry-pick Test_reverse_sort_uniq() change from patch 8.2.0183.
Make uniq() error behavior consistent with sort().
Cherry-pick Test_set_ttytype() change from patch 8.1.1826.
Cherry-pick quickfix checks from patch 8.1.2373 to test_preview.vim.
Test_viminfo_error() is applicable.
Cherry-pick E1058 from patch 8.2.0149 and port Test_deep_nest() to Lua.

Problem:    Cannot get window type for autocmd and preview window.
Solution:   Add types to win_gettype(). (Yegappan Lakshmanan, closes vim/vim#6277)
https://github.com/vim/vim/commit/0fe937fd8616fcd24b1b1ef2ab9f1657615dd22c

Cherry-pick test_preview.vim,test_window_cmd.vim changes
from patch v8.2.0522.

Problem:    ml_get error with :psearch in buffer without a name. (Dominique
            Pelle)
Solution:   Use the buffer number instead of the file name.  Check the cursor
            position.
https://github.com/vim/vim/commit/c31f9ae4f1976544522313b182957793063ee02c