Before: runtime ale_linters/slim/slimlint.vim let g:default_command = 'slim-lint %t' call ale#test#SetDirectory('/testplugin/test/command_callback') After: Restore unlet! g:default_command let g:ale_has_override = {} call ale#linter#Reset() call ale#test#RestoreDirectory() Execute(The default command should be correct): AssertEqual g:default_command, ale_linters#slim#slimlint#GetCommand(bufnr('')) Execute(The command should have the .rubocop.yml prepended as an env var if one exists): call ale#test#SetFilename('../slimlint-test-files/subdir/file.slim') AssertEqual \ 'SLIM_LINT_RUBUCOP_CONF=''/testplugin/test/slimlint-test-files/.rubocop.yml'' ' . g:default_command, \ ale_linters#slim#slimlint#GetCommand(bufnr('')) Execute(The command should have the .rubocop.yml prepended as an env var if one exists on win32): call ale#test#SetFilename('../slimlint-test-files/subdir/file.slim') let g:ale_has_override['win32'] = 1 AssertEqual \ 'set SLIM_LINT_RUBUCOP_CONF=''/testplugin/test/slimlint-test-files/.rubocop.yml'' && ' . g:default_command, \ ale_linters#slim#slimlint#GetCommand(bufnr(''))