Before: Save g:ale_ocaml_ocamlformat_executable Save g:ale_ocaml_ocamlformat_options " Use an invalid global executable, so we don't match it. let g:ale_ocaml_ocamlformat_executable = 'xxxinvalid' let g:ale_ocaml_ocamlformat_options = '' call ale#test#SetDirectory('/testplugin/test/fixers') After: Restore call ale#test#RestoreDirectory() Execute(The ocamlformat callback should return the correct default values): call ale#test#SetFilename('../test-files/ocaml/testfile.re') AssertEqual \ { \ 'command': ale#Escape('xxxinvalid') \ . ' --name=%s -', \ }, \ ale#fixers#ocamlformat#Fix(bufnr('')) Execute(The ocamlformat callback should include custom ocamlformat options): let g:ale_ocaml_ocamlformat_options = "-m 78" call ale#test#SetFilename('../test-files/ocaml/testfile.re') AssertEqual \ { \ 'command': ale#Escape('xxxinvalid') \ . ' ' . g:ale_ocaml_ocamlformat_options \ . ' --name=%s -', \ }, \ ale#fixers#ocamlformat#Fix(bufnr(''))