patch 8.0.1391: encoding empty string to JSON sometimes gives "null" commit https://github.com/vim/vim/commit/b29d328eb403a243431f4d0d5b360b4ac46bbc3e Author: Bram Moolenaar <Bram@vim.org> Date: Fri Dec 15 21:25:01 2017 +0100 patch 8.0.1391: encoding empty string to JSON sometimes gives "null" Problem: Encoding empty string to JSON sometimes gives "null". Solution: Handle NULL string as empty string. (closes https://github.com/vim/vim/issues/2446)

" Tests for :undo

func Test_ex_undo()
  new ex-undo
  setlocal ul=10
  exe "normal ione\n\<Esc>"
  setlocal ul=10
  exe "normal itwo\n\<Esc>"
  setlocal ul=10
  exe "normal ithree\n\<Esc>"
  call assert_equal(4, line('$'))
  undo
  call assert_equal(3, line('$'))
  undo 1
  call assert_equal(2, line('$'))
  undo 0
  call assert_equal(1, line('$'))
  quit!
endfunc