Before: call ale#assert#SetUpFixerTest('typescript', 'xo') runtime autoload/ale/handlers/xo.vim set filetype=typescript After: call ale#assert#TearDownFixerTest() Execute(The xo callback should return the correct default values): call ale#test#SetFilename('../xo-test-files/monorepo/packages/a/index.ts') AssertFixer \ { \ 'read_temporary_file': 1, \ 'command': (has('win32') ? 'node.exe ' : '') \ . ale#Escape(ale#path#Simplify(g:dir . '/../xo-test-files/monorepo/node_modules/xo/cli.js')) \ . ' --fix %t', \ } Execute(The xo callback should include custom xo options): let g:ale_typescript_xo_options = '--space' call ale#test#SetFilename('../xo-test-files/monorepo/packages/a/index.ts') AssertFixer \ { \ 'read_temporary_file': 1, \ 'command': (has('win32') ? 'node.exe ' : '') \ . ale#Escape(ale#path#Simplify(g:dir . '/../xo-test-files/monorepo/node_modules/xo/cli.js')) \ . ' --fix %t' \ . ' --space', \ } Execute(--stdin should be used when xo is new enough): let g:ale_typescript_xo_options = '--space' call ale#test#SetFilename('../xo-test-files/monorepo/packages/a/index.ts') GivenCommandOutput ['0.30.0'] AssertFixer \ { \ 'command': (has('win32') ? 'node.exe ' : '') \ . ale#Escape(ale#path#Simplify(g:dir . '/../xo-test-files/monorepo/node_modules/xo/cli.js')) \ . ' --stdin --stdin-filename %s' \ . ' --fix' \ . ' --space', \ }