Introduce service for merge request pipeline creation

We don't have a way to create MR pipeline today, this is one
of the headaches for users.
This change is a preliminary work for the capability.

1 files changed, 71 insertions, 0 deletions

diff --git a/spec/services/merge_requests/create_pipeline_service_spec.rb b/spec/services/merge_requests/create_pipeline_service_spec.rb
new file mode 100644
index 00000000000..9479439bde8
--- /dev/null
+++ b/spec/services/merge_requests/create_pipeline_service_spec.rb
@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MergeRequests::CreatePipelineService do
+  set(:project) { create(:project, :repository) }
+  set(:user) { create(:user) }
+  let(:service) { described_class.new(project, user, params) }
+  let(:params) { {} }
+
+  before do
+    project.add_developer(user)
+  end
+
+  describe '#execute' do
+    subject { service.execute(merge_request) }
+
+    before do
+      stub_ci_pipeline_yaml_file(YAML.dump(config))
+    end
+
+    let(:config) do
+      { rspec: { script: 'echo', only: ['merge_requests'] } }
+    end
+
+    let(:merge_request) do
+      create(:merge_request,
+        source_branch: 'feature',
+        source_project: project,
+        target_branch: 'master',
+        target_project: project)
+    end
+
+    it 'creates a detached merge request pipeline' do
+      expect { subject }.to change { Ci::Pipeline.count }.by(1)
+
+      expect(subject).to be_persisted
+      expect(subject).to be_detached_merge_request_pipeline
+    end
+
+    context 'when service is called multiple times' do
+      it 'creates a pipeline once' do
+        expect do
+          service.execute(merge_request)
+          service.execute(merge_request)
+        end.to change { Ci::Pipeline.count }.by(1)
+      end
+
+      context 'when allow_duplicate option is true' do
+        let(:params) { { allow_duplicate: true } }
+
+        it 'creates pipelines multiple times' do
+          expect do
+            service.execute(merge_request)
+            service.execute(merge_request)
+          end.to change { Ci::Pipeline.count }.by(2)
+        end
+      end
+    end
+
+    context 'when .gitlab-ci.yml does not have only: [merge_requests] keyword' do
+      let(:config) do
+        { rspec: { script: 'echo' } }
+      end
+
+      it 'does not create a pipeline' do
+        expect { subject }.not_to change { Ci::Pipeline.count }
+      end
+    end
+  end
+end