Fix custome serializer setting

The serializer should be set up in `after_initialize` so that it work
properly even if the user specifies serializer with initializers.

Also, since `custom_serializers` is `Array`, it needs to be flattened
before setting the value.

1 files changed, 12 insertions, 0 deletions

diff --git a/railties/test/application/configuration_test.rb b/railties/test/application/configuration_test.rb
index 236d73d5fd..caadae3136 100644
--- a/railties/test/application/configuration_test.rb
+++ b/railties/test/application/configuration_test.rb
@@ -1940,6 +1940,18 @@ module ApplicationTests
       assert_equal Digest::SHA1, ActiveSupport::Digest.hash_digest_class
     end
 
+    test "custom serializers should be able to set via config.active_job.custom_serializers in an initializer" do
+      class ::DummySerializer < ActiveJob::Serializers::ObjectSerializer; end
+
+      app_file "config/initializers/custom_serializers.rb", <<-RUBY
+      Rails.application.config.active_job.custom_serializers << DummySerializer
+      RUBY
+
+      app "development"
+
+      assert_includes ActiveJob::Serializers.serializers, DummySerializer
+    end
+
     private
       def force_lazy_load_hooks
         yield # Tasty clarifying sugar, homie! We only need to reference a constant to load it.