Refact build queue service tests to improve readability

spec/services/ci/update_build_queue_service_spec.rb

@@ -8,10 +8,15 @@ RSpec.describe Ci::UpdateBuildQueueService do
   let(:pipeline) { create(:ci_pipeline, project: project) }
 
   describe '#push' do
-    it 'creates a new pending build in transaction' do
-      transition = double(to: 'pending')
+    let(:transition) { double('transition') }
+
+    before do
+      allow(transition).to receive(:to).and_return('pending')
       allow(transition).to receive(:within_transaction).and_yield
+    end
 
+    context 'when pending build can be created' do
+      it 'creates a new pending build in transaction' do
         queued = subject.push(build, transition)
 
         expect(queued.build).to eq build
@@ -20,8 +25,6 @@ RSpec.describe Ci::UpdateBuildQueueService do
 
       it 'increments queue push metric' do
         metrics = spy('metrics')
-      transition = double(to: 'pending')
-      allow(transition).to receive(:within_transaction).and_yield
 
         described_class.new(metrics).push(build, transition)
 
@@ -29,21 +32,32 @@ RSpec.describe Ci::UpdateBuildQueueService do
           .to have_received(:increment_queue_operation)
           .with(:build_queue_push)
       end
+    end
 
-    it 'raises an error when invalid transition is detected' do
-      transition = double(to: 'created')
+    context 'when invalid transition is detected' do
+      it 'raises an error' do
+        allow(transition).to receive(:to).and_return('created')
 
         expect { subject.push(build, transition) }
           .to raise_error(described_class::InvalidQueueTransition)
       end
     end
+  end
 
   describe '#pop' do
-    it 'removes pending build in a transaction' do
-      transition = double(from: 'pending')
+    let(:transition) { double('transition') }
+
+    before do
+      allow(transition).to receive(:from).and_return('pending')
       allow(transition).to receive(:within_transaction).and_yield
+    end
+
+    context 'when pending build exists' do
+      before do
         Ci::PendingBuild.create!(build: build, project: project)
+      end
 
+      it 'removes pending build in a transaction' do
         dequeued = subject.pop(build, transition)
 
         expect(dequeued.build).to eq build
@@ -53,9 +67,6 @@ RSpec.describe Ci::UpdateBuildQueueService do
 
       it 'increments queue pop metric' do
         metrics = spy('metrics')
-      transition = double(from: 'pending')
-      allow(transition).to receive(:within_transaction).and_yield
-      Ci::PendingBuild.create!(build: build, project: project)
 
         described_class.new(metrics).pop(build, transition)
 
@@ -63,23 +74,25 @@ RSpec.describe Ci::UpdateBuildQueueService do
           .to have_received(:increment_queue_operation)
           .with(:build_queue_pop)
       end
+    end
 
+    context 'when pending build does not exist' do
       it 'does nothing if there is no pending build to remove' do
-      transition = double(from: 'pending')
-      allow(transition).to receive(:within_transaction).and_yield
-
         dequeued = subject.pop(build, transition)
 
         expect(dequeued).to be_nil
       end
+    end
 
-    it 'raises an error when invalid transition is detected' do
-      transition = double(from: 'created')
+    context 'when invalid transition is detected' do
+      it 'raises an error' do
+        allow(transition).to receive(:from).and_return('created')
 
         expect { subject.pop(build, transition) }
           .to raise_error(described_class::InvalidQueueTransition)
       end
     end
+  end
 
   describe '#tick' do
     shared_examples 'refreshes runner' do