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