RSpec beginner

Currently developing applications using ruby ​​on rails
I didn't know about the test code until then, so I just wrote the code.
So I thought I'd write a test code, but when I was looking at how to write a RSpec test, etc.

rails g rspec: model user

I generate a User model and test it, but like me

rails g model User

If i have already generated a model without writing test code
Can the model be tested?