Verify arguments match mailer in HaveEnqueuedMail

Guards against false-positives where both the implementation
and have_enqueued_mail matchers are passed the wrong arguments
which don't match the mailer's signature.

Author: odlp

lib/rspec/rails/matchers/have_enqueued_mail.rb

@@ -89,8 +89,19 @@ def arguments_match?(job)
           super(job)
         end
 
-        def verify_arguments_match_signature!(_job, _args)
-          # Not implemented for mailers
+        def verify_arguments_match_signature!(job, args)
+          return if @method_name.nil?
+
+          mailer_method = mailer_class_name.constantize.public_instance_method(@method_name)
+          mailer_args = args - base_mailer_args
+
+          if parameterized_mail?(job)
+            mailer_args = mailer_args[1..-1] # ignore parameterized params
+          elsif mailer_args.last.is_a?(Hash) && mailer_args.last.key?(:args)
+            mailer_args = args.last[:args]
+          end
+
+          verify_signature!(mailer_method, mailer_args)
         end
 
         def base_mailer_args

spec/rspec/rails/matchers/have_enqueued_mail_spec.rb

@@ -243,6 +243,14 @@ def test_email; end
       }.not_to have_enqueued_mail(TestMailer, :email_with_args).with(3, 4)
     end
 
+    it "fails if the arguments do not match the mailer method's signature" do
+      expect {
+        expect {
+          TestMailer.email_with_args(1).deliver_later
+        }.to have_enqueued_mail(TestMailer, :email_with_args).with(1)
+      }.to raise_error(ArgumentError, /Wrong number of arguments/)
+    end
+
     it "generates a failure message" do
       expect {
         expect { }.to have_enqueued_email(TestMailer, :test_email)
@@ -388,6 +396,14 @@ def self.name; "NonMailerJob"; end
           TestMailer.with('foo' => 'bar').email_with_args(1, 2).deliver_later
         }.to have_enqueued_mail(TestMailer, :email_with_args).with({ 'foo' => 'bar' }, 1, 2)
       end
+
+      it "fails if the arguments do not match the mailer method's signature" do
+        expect {
+          expect {
+            TestMailer.with('foo' => 'bar').email_with_args(1).deliver_later
+          }.to have_enqueued_mail(TestMailer, :email_with_args).with({ 'foo' => 'bar' }, 1)
+        }.to raise_error(ArgumentError, /Wrong number of arguments/)
+      end
     end
 
     context 'mailer job is unified', skip: !RSpec::Rails::FeatureCheck.has_action_mailer_unified_delivery? do
@@ -435,6 +451,16 @@ def self.name; "NonMailerJob"; end
           UnifiedMailerWithDeliveryJobSubClass.test_email.deliver_later
         }.to have_enqueued_mail(UnifiedMailerWithDeliveryJobSubClass, :test_email)
       end
+
+      it "fails if the arguments do not match the mailer method's signature" do
+        expect {
+          expect {
+            UnifiedMailer.with('foo' => 'bar').email_with_args(1).deliver_later
+          }.to have_enqueued_mail(UnifiedMailer, :email_with_args).with(
+            a_hash_including(params: { 'foo' => 'bar' }, args: [1])
+          )
+        }.to raise_error(ArgumentError, /Wrong number of arguments/)
+      end
     end
   end
 end