Since we updated our application to Rails 4.2, our mailer tests seems to fail (or not) randomly.
Simplified mailer code:
class ReservationMailer < ActionMailer::Base default from: ‘no-reply@1.de’, bcc: ‘kopie@1.de’
def reservation_received(reservation) @reservation = reservation @product = reservation.product
mail to: @reservation.email,
end end
Simplified test code:
reservation = Reservation.new(email: ‘max@mustermann.com’, product: product)
email = ReservationMailer.reservation_received(reservation).deliver_now
assert_equal 1, ActionMailer::Base.deliveries.size
There are some more mailers very similar to this mailer and the tests seem to fail randomly.
That means, sometimes just one of these tests fail, sometimes two and somewhen nothing fails.
I couldn’t figure out any problem, but maybe you can help me out 
