Before: Save g:ale_google_java_format_executable " Use an invalid global executable, so we don't match it. let g:ale_google_java_format_executable = 'xxxinvalid' call ale#test#SetDirectory('/testplugin/test/fixers') After: Restore call ale#test#RestoreDirectory() Execute(The google-java-format callback should return 0 when the executable isn't executable): AssertEqual \ 0, \ ale#fixers#google_java_format#Fix(bufnr('')) Execute(The google-java-format callback should run the command when the executable test passes): let g:ale_google_java_format_executable = has('win32') ? 'cmd' : 'echo' AssertEqual \ { \ 'read_temporary_file': 1, \ 'command': ale#Escape(ale_google_java_format_executable) . ' --replace %t' \ }, \ ale#fixers#google_java_format#Fix(bufnr(''))