code: function(i) {
          if (expected[i] == undefined) return 'exception'
          switch (expected[i].constructor) {
            case RegExp   : return 'exception matching ' + puts(expected[i])
            case String   : return 'exception of ' + puts(expected[i])
            case Function : return expected[i].name || 'Error'
          }
        }
docs: TODO: refactor when actual is not in expected [0]