Before: Save g:ale_crystal_format_executable Save g:ale_crystal_format_options " Use an invalid global executable, so we don't match it. let g:ale_crystal_format_executable = 'xxxinvalid' let g:ale_crystal_format_options = '' call ale#test#SetDirectory('/testplugin/test/fixers') After: Restore call ale#test#RestoreDirectory() Execute(The crystal format callback should return the correct default values): AssertEqual \ { \ 'command': ale#Escape('xxxinvalid') . ' tool format -', \ }, \ ale#fixers#crystal#Fix(bufnr('')) Execute(The crystal format callback should include custom options): let g:ale_crystal_format_options = "-list=true" AssertEqual \ { \ 'command': ale#Escape('xxxinvalid') \ . ' tool format ' . g:ale_crystal_format_options \ . ' -', \ }, \ ale#fixers#crystal#Fix(bufnr(''))