til/rails/make-action-mailer-synchronous-in-test.md

Make ActionMailer Synchronous In Test

When you set up an ActionMailer email, the default configuration is for it to use ActiveJob to send the emails. As of Rails 5, it will do so asynchronously.. Depending on your preferences for testing emails, you may prefer ActiveJob to send the emails synchronously. This can be done by changing the queue_adapter back to :inline in your config/environments/test.rb.

config.active_job.queue_adapter = :inline

If you also configure the delivery_method as :test:

config.action_mailer.delivery_method = :test

then emails will be queued up in ActionMailer::Base.deliveries allowing you to write a test like this:

expect(ActionMailer::Base.deliveries.count).to eq(1)

Check out the docs for more on ActionMailer.

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