Before: Save g:ale_hurl_hurlfmt_executable " Use an invalid global executable, so we don't match it. let g:ale_hurl_hurlfmt_executable = 'xxxinvalid' call ale#test#SetDirectory('/testplugin/test/fixers') After: Restore call ale#test#RestoreDirectory() Execute(The hurlfmt callback should return the correct default values): call ale#test#SetFilename('../test-files/hurl/dummy.hurl') AssertEqual \ { \ 'command': ale#Escape(g:ale_hurl_hurlfmt_executable) \ . ' --out hurl', \ }, \ ale#fixers#hurlfmt#Fix(bufnr(''))