Problem:    Spell test fails because error message changed.
Solution:   Adjust expected error message.

Problem:    Using reduce() on a list from range() is a bit slow.
Solution:   Avoid materializing the list.

Problem:    SpellFileMissing autocmd may delete buffer.
Solution:   Disallow deleting the current buffer to avoid using freed memory.

Problem:    Running source tests leaves file behind.
Solution:   Add the "D" flag to writefile(). (Dominique Pellé, closes #11243)
            Also do this for other writefile() calls and drop delete().

Problem:    Blockedit test passes with wrong result.
Solution:   Add a "vim9script" line to make indenting work.

Problem:    Tests delete files with a separate delete() call.
Solution:   Use deferred delete.

Problem:    Global interrupt test fails when run under valgrind.
Solution:   Use TermWait().

Problem:    Blockedit test fails because of wrong indent.
Solution:   Adjust the expected text temporarily

Problem:    With spell checking, deleting a full stop at the end of a line
            does not update SpellCap at the start of the next line.
Solution:   Update the next line when characters have been deleted.  Also when
            using undo.