Problem:    Some test failures don't give a clear error.
Solution:   Use assert_match() and assert_fails() instead of assert_true().
            (Ken Takata, closes vim/vim#7368)
https://github.com/vim/vim/commit/5dc4e2f883896c99ebe83355822ac6067970b031

Problem:    No 'backspace' value allows ignoring the insertion point.
Solution:   Add the "nostop" and 3 values. (Christian Brabandt, closes vim/vim#5940)
https://github.com/vim/vim/commit/aa0489e12d227d24752cf16e4e97058ac32edcc1

Porting it to test/functional/legacy/backspace_opt_spec.lua
was a mistake.
Tests pass after commenting out some lines for Vi compatibility.

File is copied from Vim as of patch v8.2.0540.
Patch v8.2.0540 cannot be fully ported yet.
This file is a prequisite for future v8.2.x patches.