Before: call ale#assert#SetUpFixerTest('javascript', 'prettier_standard') After: call ale#assert#TearDownFixerTest() Execute(The prettier callback should return the correct default values): call ale#test#SetFilename('../test-files/prettier/testfile.js') AssertFixer \ { \ 'command': ale#Escape(g:ale_javascript_prettier_standard_executable) \ . ' --stdin' \ . ' --stdin-filepath=%s ', \ }