Merge branch 'js/add-i-a-bit-more-tests'

Merge branch 'js/add-i-a-bit-more-tests'

Test coverage update in preparation for further work on "git add -i".

* js/add-i-a-bit-more-tests:
  apply --allow-overlap: fix a corner case
  git add -p: use non-zero exit code when the diff generation failed
  t3701: verify that the diff.algorithm config setting is handled
  t3701: verify the shown messages when nothing can be added
  t3701: add a test for the different `add -p` prompts
  t3701: avoid depending on the TTY prerequisite
  t3701: add a test for advanced split-hunk editing