How to access activation_token in integration test?

A controller method that processes a joined signup calls upon a model method that creates a value for activation_token for the user. But how can I access that value in an integration test such as the one below?

The controller method basically comes down to if everything saved @user.create_token end. And the model method is:

def create_token
  self.activation_token  = User.new_token
  self.activation_digest = User.digest(activation_token)
  update_attribute(:activation_digest, self.activation_digest)
  update_columns(activation_sent_at: Time.zone.now)
end

The above works but how can I access the activation_token in an integration test:

assert_difference ['Organization.count', 'User.count'], 1 do
  post organizations_path, 
    organization: { name: "Abc1",
                    users_attributes: { "0" => { email: "adef1@uniqu.br",
                                                 username: "adef111",
                                                 admin: true,
                                                 password: "foobar",
                                                 password_confirmation: "foobar"} } }
end
assert_equal 1, ActionMailer::Base.deliveries.size
organization = assigns(:organization)
user = organization.users.first
# how can I then here access the activation_token? user.activation_token does not work.