Make ActiveJob tests runnable with bin/test again

A few things:
* Removal of delayed_job in the Gemfile causes a load error. CI is fine since this file is filtered out in the rake task
* The async adapter test assumes the async adapter to be present. Again not a problem on CI, but the default is the inline adapter
* Integration tests are run, they reference a job that is present only in the dummy app

Author: Earlopain

activejob/test/cases/async_adapter_test.rb

@@ -1,9 +1,10 @@
 # frozen_string_literal: true
 
 require "helper"
-require "active_job/queue_adapters/async_adapter"
 require "jobs/hello_job"
 
+return unless adapter_is?(:async)
+
 class AsyncAdapterTest < ActiveSupport::TestCase
   setup do
     JobBuffer.clear

activejob/test/cases/delayed_job_adapter_test.rb

@@ -1,10 +1,11 @@
 # frozen_string_literal: true
 
 require "helper"
-require "active_job/queue_adapters/delayed_job_adapter"
 require "jobs/disable_log_job"
 require "jobs/hello_job"
 
+return unless adapter_is?(:delayed_job)
+
 class DelayedJobAdapterTest < ActiveSupport::TestCase
   test "does not log arguments when log_arguments is set to false on a job" do
     job_id = SecureRandom.uuid

activejob/test/integration/queuing_test.rb

@@ -6,6 +6,8 @@
 require "jobs/provider_jid_job"
 require "active_support/core_ext/numeric/time"
 
+return unless ENV["AJ_INTEGRATION_TESTS"] == "1"
+
 class QueuingTest < ActiveSupport::TestCase
   test "should run jobs enqueued on a listening queue" do
     TestJob.perform_later @id