DEV: make Jobs.enqueue tests less fragile

Previously we depended on non Sidekiq specific mocking which is not the
official way of testing Sidekiq, this made these tests very fragile

New testing is more robust and complete

spec/jobs/jobs_spec.rb

@@ -11,13 +11,40 @@ describe Jobs do
       end
 
       it 'enqueues a job in sidekiq' do
-        Sidekiq::Client.expects(:enqueue).with(Jobs::ProcessPost, post_id: 1, current_site_id: 'default')
-        Jobs.enqueue(:process_post, post_id: 1)
+        Sidekiq::Testing.fake! do
+          jobs = Jobs::ProcessPost.jobs
+
+          jobs.clear
+          Jobs.enqueue(:process_post, post_id: 1)
+          expect(jobs.length).to eq(1)
+          job = jobs.first
+
+          expected = {
+            "class" => "Jobs::ProcessPost",
+            "args" => [{ "post_id" => 1, "current_site_id" => "default" }],
+            "queue" => "default"
+          }
+          expect(job.slice("class", "args", "queue")).to eq(expected)
+        end
       end
 
       it "does not pass current_site_id when 'all_sites' is present" do
-        Sidekiq::Client.expects(:enqueue).with(Jobs::ProcessPost, post_id: 1)
-        Jobs.enqueue(:process_post, post_id: 1, all_sites: true)
+        Sidekiq::Testing.fake! do
+          jobs = Jobs::ProcessPost.jobs
+
+          jobs.clear
+          Jobs.enqueue(:process_post, post_id: 1, all_sites: true)
+
+          expect(jobs.length).to eq(1)
+          job = jobs.first
+
+          expected = {
+            "class" => "Jobs::ProcessPost",
+            "args" => [{ "post_id" => 1 }],
+            "queue" => "default"
+          }
+          expect(job.slice("class", "args", "queue")).to eq(expected)
+        end
       end
 
       it "doesn't execute the job" do
@@ -27,10 +54,23 @@ describe Jobs do
       end
 
       it "should enqueue with the correct database id when the current_site_id option is given" do
-        Sidekiq::Client.expects(:enqueue).with do |arg1, arg2|
-          arg2[:current_site_id] == 'test_db' && arg2[:sync_exec].nil?
+
+        Sidekiq::Testing.fake! do
+          jobs = Jobs::ProcessPost.jobs
+
+          jobs.clear
+          Jobs.enqueue(:process_post, post_id: 1, current_site_id: 'test_db')
+
+          expect(jobs.length).to eq(1)
+          job = jobs.first
+
+          expected = {
+            "class" => "Jobs::ProcessPost",
+            "args" => [{ "post_id" => 1, "current_site_id" => "test_db" }],
+            "queue" => "default"
+          }
+          expect(job.slice("class", "args", "queue")).to eq(expected)
         end
-        Jobs.enqueue(:process_post, post_id: 1, current_site_id: 'test_db')
       end
     end