Before: Save g:ale_dhall_executable Save g:ale_dhall_options " Use an invalid global executable, so we don’t match it. let g:ale_dhall_executable = 'odd-dhall' let g:ale_dhall_options = '--ascii' call ale#assert#SetUpFixerTest('dhall-format', 'dhall-format') After: call ale#assert#TearDownFixerTest() Execute(The dhall-format callback should return the correct options): call ale#test#SetFilename('../dhall_files/testfile.dhall') AssertFixer \ { \ 'command': ale#Escape('odd-dhall') \ . ' --ascii' \ . ' format' \ . ' --inplace %t', \ 'read_temporary_file': 1, \ }