     home: () ->
       # The home button is the parent of the home icon.
       @select('button .glyphicon-home', '..').then (button) =>
-        expect(button).to.exist
+        expect(button, 'The home button is missing').to.exist
         # Go home...
         button.click().then =>
           # ...grab the URL...

    help: () ->
      @select('.qi-help').then (block) =>
        # Help is initially hidden.
        expect(block.isDisplayed()).to.eventually.be.false
        # The help button is the parent of the question mark icon.
        @select('button .glyphicon-question-sign', '..').then (button) =>
          expect(button).to.exist
          # Open the help view...
          button.click().then =>
            # ...verify that the help is displayed...
            expect(block.isDisplayed()).to.eventually.be.true
            # ...find the element...
            @select('.qi-main .qi-help-text').then (content) =>
              # ...resolve to the formatted help content.

    #   element, or null if no such element is found
    select: (selectors...) ->
      # page.select(...) delegates to select(page, ...)
      # in this module's outer scope.
      select(this, selectors...)

    # @param selectors the target search selectors
