No, you cannot take the GED test entirely online. While some GED preparation materials and practice tests are available online, the actual GED test itself requires you to go to an official GED testing center. These centers are physical locations where you'll take the exam under proctored conditions.
There is no legitimate website offering the full GED test online. Beware of any website claiming to offer this; they are likely scams. To find an official GED testing center near you, you should visit the official GED Testing Service website.