Actionmailer - heroku app

Actionmailer - heroku app

This is a newbie question so please excuse me, I have been working with
rails, but this is the first time i am trying to require gems from a
heroku app that does not include rails - just a plain Ruby app. ok I have
a app.rb file looking like this:
require "sinatra"
require 'koala'
require 'action_mailer'
ActionMailer::Base.raise_delivery_errors = true
ActionMailer::Base.delivery_method = :smtp
ActionMailer::Base.smtp_settings = {
:address => "smtp.sendgrid.net",
:port => 587,
:domain => "MYDOMAIN",
:authentication => :plain,
:user_name => "USER_NAME",
:password => "PASSWORD",
:enable_starttls_auto => true
}
ActionMailer::Base.view_paths= File.dirname(__FILE__)
class TestMailer < ActionMailer::Base
default :from => "MY_EMAIL"
def welcome_email
mail(:to => "MY_EMAIL", :subject => "Test mail", :body => "Test mail
body")
end
end
What I would like to do is run
TestMailer::deliver_test_email
in the console and get the details or run
TestMailer::deliver_test_email.deliver
to send a test email
but all i get is :
NameError: uninitialized constant Object::TestMailer
I have included actionmailer in the Gemfile and its also in the Gemfile.lock
I am sure it is something straight forward for an experienced Ruby dev,
but I am struggling could anyone help me please?
Thanks