If you have content inside a page that is hidden by CSS, the following will work with Selenium, but not when using the Rack::Test driver. The Selenium driver correctly only considers text that is actually visible to a user.

Then I should not see "foobear"

UI/UX Design by

We make sure that your target audience has the best possible experience with your digital product. You get:

• Design tailored to your audience
• Proven processes customized to your needs
• An expert team of experienced designers

Read more Show archive.org snapshot

This is because the Rack::Test driver does not know if an element is visible, and only looks at the DOM.

Spreewald Show archive.org snapshot offers steps to check that an element is hidden by CSS:

Then "foo" should be hidden

You can also check that an element is visible:

Then "foo" should be visible

Implementation details

• Regardless of whether we expect the text to be visible or hidden, we always expect the given text to be contained in the HTML. The test is about whether or not it is hidden via CSS.
• In a Selenium scenario, visibility is detected via Javascript. This detection is very precise and should correctly determine visibility for the most fucked up cases. The steps have support for jQuery and Prototype projects.
• In a standard, non-Selenium Rack::Test scenario, the steps are considerably less clever. Here they consider a text hidden if it sits in a container with a hidden or style="display: none" attribute. In a Rack::Test scenario the step will not recognize if the element is hidden via another CSS class.