Do we need to test every single thing?

I am finally convinced with the idea of outside-in approach of testing and also the way Jeffrey and Adam Wathan do their tests. If I am not mistaken, they test with the outside-in approach but now my problem is, when I get to the lower level (Unit), do I need to test everything? for example:

a_user_has_name

a_user_has_username

a_user_has_email

a_user_has_is_active

a_user_has_location

a_user_has_locale ....

Another thing that comes to my mind is that, Yes I need to test all properties but putting them in one test like a_user_may_be_created and then assert that it has all the properties?

Please advice