Before: Save g:ale_command_wrapper runtime autoload/ale/lsp.vim let g:ale_command_wrapper = '' let g:args = [] " Mock the StartProgram function so we can just capture the arguments. function! ale#lsp#StartProgram(...) abort let g:args = a:000[1:] endfunction After: Restore unlet! g:args runtime autoload/ale/lsp.vim Execute(Command formatting should be applied correctly for LSP linters): call ale#lsp_linter#StartLSP( \ bufnr(''), \ { \ 'name': 'linter', \ 'language': {-> 'x'}, \ 'project_root': {-> '/foo/bar'}, \ 'lsp': 'stdio', \ 'executable': has('win32') ? 'cmd': 'true', \ 'command': '%e --foo', \ }, \ {-> 0} \) if has('win32') AssertEqual \ ['cmd', 'cmd /s/c "cmd --foo"'], \ g:args else AssertEqual \ ['true', [&shell, '-c', '''true'' --foo']], \ g:args endif