Hi Deborah,
Are you sure that the test you are looking for were shared to commons? You should probably check with whomever is supposed to have shared them to see what settings they applied. When someone shares something to the Canvas Commons they have the ability to share just with themselves; just with their school, just with a group of people from their school, or even to the entire community of Canvas users.
Regarding the subject line of your request with respect to "students" accessing the test.... students normally do not have access to the Canvas Commons. Only people who have teacher access to at least one course can typicallly search the Canvas Commons from the link in your Canvas instance and import the content into courses.
If you'd like a little more information about how the Canvas Commons work, here is a quick guide https://community.canvaslms.com/docs/DOC-16712-4152725288
Rick
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