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' call ale#test#SetDirectory('/testplugin/test/fixers') silent cd .. silent cd command_callback let g:dir = getcwd() let b:bin_dir = has('win32') ? 'Scripts' : 'bin' After: Restore unlet! b:bin_dir call ale#test#RestoreDirectory() Execute(The yapf callback should return the correct default values): AssertEqual \ 0, \ ale#fixers#yapf#Fix(bufnr('')) call ale#test#SetFilename('python_paths/with_virtualenv/subdir/foo/bar.py') AssertEqual \ {'command': ale#Escape(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/env/' . b:bin_dir . '/yapf'))}, \ ale#fixers#yapf#Fix(bufnr('')) \ Execute(The yapf should include the .style.yapf file if present): call ale#test#SetFilename('python_paths/with_virtualenv/dir_with_yapf_config/foo/bar.py') AssertEqual \ { \ 'command': \ ale#Escape(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/env/' . b:bin_dir . '/yapf')) \ . ' --no-local-style' \ . ' --style ' . ale#Escape(ale#path#Simplify(g:dir . '/python_paths/with_virtualenv/dir_with_yapf_config/.style.yapf')), \ }, \ ale#fixers#yapf#Fix(bufnr(''))