In order for an exam to be shared with Google Classroom, the exam first have to be connected to Google Classroom. Read more about it here.

Publish the exam key in Google Classroom

Students can be given the exam key in multiple ways, just like with any other exam, but when connecting the exam to Google Classroom, you will also have the choice to publish the exam key and a link to the exam in the Google Classroom feed.

You do this by entering the monitoring view in Exam.net and clicking on the Exam Key button, where you choose “Publish link in Google Classroom”

The students in the chosen class will receive an email containing a link to the Google Classroom feed. From the feed, they can enter the exam.

Connect to high-security exam on Chromebook (Kiosk application)

However, If students are supposed to connect to an exam via the kiosk application (Chromebooks), they must manually enter the exam key inside the kiosk application since the kiosk app is only available on the Chromebook sign-in screen. 

Related articles

Connecting an exam to Google Classroom

Conducting an exam connected to Google Classroom

After the exam - export and manage in Google Classroom

The student's view in Google Classroom

More information about Google Classroom...

...can be found on Google Classroom's support pages: https://support.google.com/edu/classroom/