commit https://github.com/vim/vim/commit/73dfe917ba6357413aaf98a021c91add5ac6e9bc Author: Bram Moolenaar <Bram@vim.org> Date: Sat Apr 23 13:54:48 2016 +0200 patch 7.4.1779 Problem: Using negative index in strcharpart(). (Yegappan Lakshmanan) Solution: Assume single byte when using a negative iindex.

" Test for joining lines.

func Test_join_with_count()
  new
  call setline(1, ['one', 'two', 'three', 'four'])
  normal J
  call assert_equal('one two', getline(1))
  %del
  call setline(1, ['one', 'two', 'three', 'four'])
  normal 10J
  call assert_equal('one two three four', getline(1))
  quit!
endfunc