Difference between let and def

Question

I wonder between method and let definition inside rspec describe block? Why should I use let instead def?

let(:create_user) { post :create }

Vs

def create_user
  post :create
end

Both ways seems to work the same inside the test:

expect { create_user }.to change { User.count }.by(1)

Answer 1

Not sure if it is the only difference, but let memoizes it's value. So it would be closer to:

def create_user
  @_create_user ||= post :create
end