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