Yes, it is. But not only Selenium, we want to add other drivers to Selenium, so it'll be easy to change between drivers, or use more than one driver. Selenium is little slow, so you can use zope.testbrowser for tests that don't deal with JavaScript.
Imagine you're starting and don't have to worry about JavaScript, you can start testing using the zope.testbrowser driver. Then, if you start needing to test JavaScript-based components, or for another reason you need to actually open the browser, all you need to do is change the driver.
Regards,
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Francisco Souza