Before: Save g:ale_html_tidy_executable let g:ale_html_tidy_executable = 'tidy_paths/tidy' 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 tidy callback should return 0 if tidy not found): let g:ale_html_tidy_executable = 'xxxinvalidpath' AssertEqual \ 0, \ ale#fixers#tidy#Fix(bufnr('')) Execute(The tidy callback should return the correct default command): AssertEqual \ { \ 'command': ale#Escape('tidy_paths/tidy') \ . ' -q --tidy-mark no --show-errors 0 --show-warnings 0' \ }, \ ale#fixers#tidy#Fix(bufnr(''))