Add assert_enqueued_emails and assert_no_enqueued_emails

actionmailer/CHANGELOG.md

+*   Add `assert_enqueued_emails` and `assert_no_enqueued_emails`.
+
+        def test_emails
+          assert_enqueued_emails 2 do
+            ContactMailer.welcome.deliver_later
+            ContactMailer.welcome.deliver_later
+          end
+        end
+
+        def test_no_emails
+          assert_no_enqueued_emails do
+            # No emails enqueued here
+          end
+        end
+
+    *George Claghorn*
+
 *   Add `_mailer` suffix to mailers created via generator, following the same
     naming convention used in controllers and jobs.
 

actionmailer/lib/action_mailer/test_helper.rb

+require 'active_job'
+
 module ActionMailer
   # Provides helper methods for testing Action Mailer, including #assert_emails
   # and #assert_no_emails
   module TestHelper
+    include ActiveJob::TestHelper
+
     # Asserts that the number of emails sent matches the given number.
     #
     #   def test_emails
@@ -58,5 +62,52 @@ def assert_emails(number)
     def assert_no_emails(&block)
       assert_emails 0, &block
     end
+
+    # Asserts that the number of emails enqueued for later delivery matches
+    # the given number.
+    #
+    #   def test_emails
+    #     assert_enqueued_emails 0
+    #     ContactMailer.welcome.deliver_later
+    #     assert_enqueued_emails 1
+    #     ContactMailer.welcome.deliver_later
+    #     assert_enqueued_emails 2
+    #   end
+    #
+    # If a block is passed, that block should cause the specified number of
+    # emails to be enqueued.
+    #
+    #   def test_emails_again
+    #     assert_enqueued_emails 1 do
+    #       ContactMailer.welcome.deliver_later
+    #     end
+    #
+    #     assert_enqueued_emails 2 do
+    #       ContactMailer.welcome.deliver_later
+    #       ContactMailer.welcome.deliver_later
+    #     end
+    #   end
+    def assert_enqueued_emails(number, &block)
+      assert_enqueued_jobs number, only: ActionMailer::DeliveryJob, &block
+    end
+
+    # Asserts that no emails are enqueued for later delivery.
+    #
+    #   def test_no_emails
+    #     assert_no_enqueued_emails
+    #     ContactMailer.welcome.deliver_later
+    #     assert_enqueued_emails 1
+    #   end
+    #
+    # If a block is provided, it should not cause any emails to be enqueued.
+    #
+    #   def test_no_emails
+    #     assert_no_enqueued_emails do
+    #       # No emails should be enqueued from this block
+    #     end
+    #   end
+    def assert_no_enqueued_emails(&block)
+      assert_no_enqueued_jobs only: ActionMailer::DeliveryJob, &block
+    end
   end
 end

actionmailer/test/test_helper_test.rb

@@ -119,6 +119,53 @@ def test_assert_no_emails_failure
 
     assert_match(/0 .* but 1/, error.message)
   end
+
+  def test_assert_enqueued_emails
+    assert_nothing_raised do
+      assert_enqueued_emails 1 do
+        TestHelperMailer.test.deliver_later
+      end
+    end
+  end
+
+  def test_assert_enqueued_emails_too_few_sent
+    error = assert_raise ActiveSupport::TestCase::Assertion do
+      assert_enqueued_emails 2 do
+        TestHelperMailer.test.deliver_later
+      end
+    end
+
+    assert_match(/2 .* but 1/, error.message)
+  end
+
+  def test_assert_enqueued_emails_too_many_sent
+    error = assert_raise ActiveSupport::TestCase::Assertion do
+      assert_enqueued_emails 1 do
+        TestHelperMailer.test.deliver_later
+        TestHelperMailer.test.deliver_later
+      end
+    end
+
+    assert_match(/1 .* but 2/, error.message)
+  end
+
+  def test_assert_no_enqueued_emails
+    assert_nothing_raised do
+      assert_no_enqueued_emails do
+        TestHelperMailer.test.deliver_now
+      end
+    end
+  end
+
+  def test_assert_no_enqueued_emails_failure
+    error = assert_raise ActiveSupport::TestCase::Assertion do
+      assert_no_enqueued_emails do
+        TestHelperMailer.test.deliver_later
+      end
+    end
+
+    assert_match(/0 .* but 1/, error.message)
+  end
 end
 
 class AnotherTestHelperMailerTest < ActionMailer::TestCase