commit https://github.com/vim/vim/commit/1000565c3a2439c9a7c9759284814dbf3b8bc20d Author: Bram Moolenaar <Bram@vim.org> Date: Thu Dec 31 21:03:23 2015 +0100 patch 7.4.1012 Problem: Vim overwrites the value of $PYTHONHOME. Solution: Do not set $PYTHONHOME if it is already set. (Kazuki Sakamoto, closes https://github.com/vim/vim/issues/500)

Test for ":options".

STARTTEST
:so small.vim
:let caught = 'ok'
:try
  :options
:catch 
  :let caught = v:throwpoint . "\n" . v:exception
:endtry
:buf 1
:$put =caught
:"
:" Test that changing 'path' keeps two commas.
:set path=foo,,bar
:set path-=bar
:set path+=bar
:$put =&path
:/^result/,$w! test.out
:qa!
ENDTEST

result