After: unlet! g:output Execute(ALEInfo -clipboard should that clipboard support is required): " When run in the Docker image, there's no clipboard support, so this test " will actually run. if !has('clipboard') let g:output = '' redir => g:output :ALEInfo -clipboard redir END AssertEqual 'clipboard not available. Try :ALEInfoToFile instead.', join(split(g:output)) endif