Before: Save g:ale_python_autopep8_executable Save g:ale_python_autopep8_options " Use an invalid global executable, so we don't match it. let g:ale_python_autopep8_executable = 'xxxinvalid' let g:ale_python_autopep8_options = '' call ale#test#SetDirectory('/testplugin/test/fixers') silent cd .. silent cd command_callback let g:dir = getcwd() After: Restore call ale#test#RestoreDirectory() Execute(The autopep8 callback should return the correct default values): AssertEqual \ 0, \ ale#fixers#autopep8#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/autopep8' -" }, \ ale#fixers#autopep8#Fix(bufnr('')) Execute(The autopep8 callback should include options): let g:ale_python_autopep8_options = '--some-option' silent execute 'file ' . fnameescape(g:dir . '/python_paths/with_virtualenv/subdir/foo/bar.py') AssertEqual \ {'command': "'" . g:dir . "/python_paths/with_virtualenv/env/bin/autopep8' --some-option -" }, \ ale#fixers#autopep8#Fix(bufnr(''))