module ActionMailer::TestHelper

Asserts that the number of emails sent matches the given number.

def test_emails
  assert_emails 0
  ContactMailer.welcome.deliver
  assert_emails 1
  ContactMailer.welcome.deliver
  assert_emails 2
end

If a block is passed, that block should cause the specified number of emails to be sent.

def test_emails_again
  assert_emails 1 do
    ContactMailer.welcome.deliver
  end

  assert_emails 2 do
    ContactMailer.welcome.deliver
    ContactMailer.welcome.deliver
  end
end

# File actionmailer/lib/action_mailer/test_helper.rb, line 26
def assert_emails(number)
  if block_given?
    original_count = ActionMailer::Base.deliveries.size
    yield
    new_count = ActionMailer::Base.deliveries.size
    assert_equal original_count + number, new_count, "#{number} emails expected, but #{new_count - original_count} were sent"
  else
    assert_equal number, ActionMailer::Base.deliveries.size
  end
end

Assert that no emails have been sent.

def test_emails
  assert_no_emails
  ContactMailer.welcome.deliver
  assert_emails 1
end

If a block is passed, that block should not cause any emails to be sent.

def test_emails_again
  assert_no_emails do
    # No emails should be sent from this block
  end
end

Note: This assertion is simply a shortcut for:

assert_emails 0

# File actionmailer/lib/action_mailer/test_helper.rb, line 56
def assert_no_emails(&block)
  assert_emails 0, &block
end