Before: Save g:ale_python_yapf_executable " Use an invalid global executable, so we don't match it. let g:ale_python_yapf_executable = 'xxxinvalid' silent! execute 'cd /testplugin/test/command_callback' silent cd .. silent cd command_callback let g:dir = getcwd() After: Restore silent execute 'cd ' . fnameescape(g:dir) " Set the file to something else, " or we'll cause issues when running other tests silent file 'dummy.py' unlet! g:dir Execute(The yapf callback should return the correct default values): AssertEqual \ 0, \ ale#fixers#yapf#Fix(bufnr('')) silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/bar.py') AssertEqual \ {'command': "'" . g:dir . "/python_paths/with_virtualenv/env/bin/yapf' --no-local-style" }, \ ale#fixers#yapf#Fix(bufnr(''))