Merge branch 'abstract-auto-merge' into 'master'

Refactor and abstract Auto Merge Processes

See merge request gitlab-org/gitlab-ce!28595

17 files changed, 306 insertions, 66 deletions

diff --git a/spec/controllers/projects/merge_requests_controller_spec.rb b/spec/controllers/projects/merge_requests_controller_spec.rb
index f4a18dcba51..f8c0ab55eb4 100644
--- a/spec/controllers/projects/merge_requests_controller_spec.rb
+++ b/spec/controllers/projects/merge_requests_controller_spec.rb
@@ -429,8 +429,9 @@ describe Projects::MergeRequestsController do
 
         it 'sets the MR to merge when the pipeline succeeds' do
           service = double(:merge_when_pipeline_succeeds_service)
+          allow(service).to receive(:available_for?) { true }
 
-          expect(MergeRequests::MergeWhenPipelineSucceedsService)
+          expect(AutoMerge::MergeWhenPipelineSucceedsService)
             .to receive(:new).with(project, anything, anything)
             .and_return(service)
           expect(service).to receive(:execute).with(merge_request)
@@ -713,9 +714,9 @@ describe Projects::MergeRequestsController do
     end
   end
 
-  describe 'POST cancel_merge_when_pipeline_succeeds' do
+  describe 'POST cancel_auto_merge' do
     subject do
-      post :cancel_merge_when_pipeline_succeeds,
+      post :cancel_auto_merge,
         params: {
           format: :json,
           namespace_id: merge_request.project.namespace.to_param,
@@ -725,14 +726,15 @@ describe Projects::MergeRequestsController do
         xhr: true
     end
 
-    it 'calls MergeRequests::MergeWhenPipelineSucceedsService' do
-      mwps_service = double
+    it 'calls AutoMergeService' do
+      auto_merge_service = double
 
-      allow(MergeRequests::MergeWhenPipelineSucceedsService)
+      allow(AutoMergeService)
         .to receive(:new)
-        .and_return(mwps_service)
+        .and_return(auto_merge_service)
 
-      expect(mwps_service).to receive(:cancel).with(merge_request)
+      allow(auto_merge_service).to receive(:available_strategies).with(merge_request)
+      expect(auto_merge_service).to receive(:cancel).with(merge_request)
 
       subject
     end
diff --git a/spec/factories/merge_requests.rb b/spec/factories/merge_requests.rb
index e8df5094b83..0b6a43b13a9 100644
--- a/spec/factories/merge_requests.rb
+++ b/spec/factories/merge_requests.rb
@@ -95,7 +95,8 @@ FactoryBot.define do
     end
 
     trait :merge_when_pipeline_succeeds do
-      merge_when_pipeline_succeeds true
+      auto_merge_enabled true
+      auto_merge_strategy AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS
       merge_user { author }
     end
 
diff --git a/spec/features/merge_request/user_merges_when_pipeline_succeeds_spec.rb b/spec/features/merge_request/user_merges_when_pipeline_succeeds_spec.rb
index d4ad11b3585..e7b92dc5535 100644
--- a/spec/features/merge_request/user_merges_when_pipeline_succeeds_spec.rb
+++ b/spec/features/merge_request/user_merges_when_pipeline_succeeds_spec.rb
@@ -74,11 +74,12 @@ describe 'Merge request > User merges when pipeline succeeds', :js do
                    source_project: project,
                    title: 'Bug NS-04',
                    author: user,
-                   merge_user: user,
-                   merge_params: { force_remove_source_branch: '1' })
+                   merge_user: user)
         end
 
         before do
+          merge_request.merge_params['force_remove_source_branch'] = '0'
+          merge_request.save!
           click_link "Cancel automatic merge"
         end
 
@@ -102,11 +103,11 @@ describe 'Merge request > User merges when pipeline succeeds', :js do
 
   context 'when merge when pipeline succeeds is enabled' do
     let(:merge_request) do
-      create(:merge_request_with_diffs, :simple,  source_project: project,
-                                                  author: user,
-                                                  merge_user: user,
-                                                  title: 'MepMep',
-                                                  merge_when_pipeline_succeeds: true)
+      create(:merge_request_with_diffs, :simple, :merge_when_pipeline_succeeds,
+        source_project: project,
+        author: user,
+        merge_user: user,
+        title: 'MepMep')
     end
     let!(:build) do
       create(:ci_build, pipeline: pipeline)
diff --git a/spec/features/merge_request/user_sees_merge_widget_spec.rb b/spec/features/merge_request/user_sees_merge_widget_spec.rb
index 93ddde623fe..1477307ed7b 100644
--- a/spec/features/merge_request/user_sees_merge_widget_spec.rb
+++ b/spec/features/merge_request/user_sees_merge_widget_spec.rb
@@ -314,7 +314,8 @@ describe 'Merge request > User sees merge widget', :js do
   context 'view merge request with MWPS enabled but automatically merge fails' do
     before do
       merge_request.update(
-        merge_when_pipeline_succeeds: true,
+        auto_merge_enabled: true,
+        auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
         merge_user: merge_request.author,
         merge_error: 'Something went wrong'
       )
diff --git a/spec/frontend/vue_mr_widget/stores/get_state_key_spec.js b/spec/frontend/vue_mr_widget/stores/get_state_key_spec.js
index b356ea85cad..0f5d47b3bfe 100644
--- a/spec/frontend/vue_mr_widget/stores/get_state_key_spec.js
+++ b/spec/frontend/vue_mr_widget/stores/get_state_key_spec.js
@@ -4,7 +4,7 @@ describe('getStateKey', () => {
   it('should return proper state name', () => {
     const context = {
       mergeStatus: 'checked',
-      mergeWhenPipelineSucceeds: false,
+      autoMergeEnabled: false,
       canMerge: true,
       onlyAllowMergeIfPipelineSucceeds: false,
       isPipelineFailed: false,
@@ -31,9 +31,9 @@ describe('getStateKey', () => {
 
     expect(bound()).toEqual('notAllowedToMerge');
 
-    context.mergeWhenPipelineSucceeds = true;
+    context.autoMergeEnabled = true;
 
-    expect(bound()).toEqual('mergeWhenPipelineSucceeds');
+    expect(bound()).toEqual('autoMergeEnabled');
 
     context.isSHAMismatch = true;
 
@@ -80,7 +80,7 @@ describe('getStateKey', () => {
   it('returns rebased state key', () => {
     const context = {
       mergeStatus: 'checked',
-      mergeWhenPipelineSucceeds: false,
+      autoMergeEnabled: false,
       canMerge: true,
       onlyAllowMergeIfPipelineSucceeds: true,
       isPipelineFailed: true,
diff --git a/spec/javascripts/vue_mr_widget/components/states/mr_widget_merge_when_pipeline_succeeds_spec.js b/spec/javascripts/vue_mr_widget/components/states/mr_widget_merge_when_pipeline_succeeds_spec.js
index b9718a78fa4..8e0415b813b 100644
--- a/spec/javascripts/vue_mr_widget/components/states/mr_widget_merge_when_pipeline_succeeds_spec.js
+++ b/spec/javascripts/vue_mr_widget/components/states/mr_widget_merge_when_pipeline_succeeds_spec.js
@@ -21,7 +21,7 @@ describe('MRWidgetMergeWhenPipelineSucceeds', () => {
         canCancelAutomaticMerge: true,
         mergeUserId: 1,
         currentUserId: 1,
-        setToMWPSBy: {},
+        setToAutoMergeBy: {},
         sha,
         targetBranchPath,
         targetBranch,
@@ -106,7 +106,7 @@ describe('MRWidgetMergeWhenPipelineSucceeds', () => {
           expect(eventHub.$emit).toHaveBeenCalledWith('MRWidgetUpdateRequested');
           expect(vm.service.merge).toHaveBeenCalledWith({
             sha,
-            merge_when_pipeline_succeeds: true,
+            auto_merge_strategy: 'merge_when_pipeline_succeeds',
             should_remove_source_branch: true,
           });
           done();
diff --git a/spec/javascripts/vue_mr_widget/components/states/mr_widget_ready_to_merge_spec.js b/spec/javascripts/vue_mr_widget/components/states/mr_widget_ready_to_merge_spec.js
index 368c997d318..3ae773b6ccb 100644
--- a/spec/javascripts/vue_mr_widget/components/states/mr_widget_ready_to_merge_spec.js
+++ b/spec/javascripts/vue_mr_widget/components/states/mr_widget_ready_to_merge_spec.js
@@ -80,7 +80,7 @@ describe('ReadyToMerge', () => {
     it('should have default data', () => {
       expect(vm.mergeWhenBuildSucceeds).toBeFalsy();
       expect(vm.useCommitMessageWithDescription).toBeFalsy();
-      expect(vm.setToMergeWhenPipelineSucceeds).toBeFalsy();
+      expect(vm.autoMergeStrategy).toBeUndefined();
       expect(vm.showCommitMessageEditor).toBeFalsy();
       expect(vm.isMakingRequest).toBeFalsy();
       expect(vm.isMergingImmediately).toBeFalsy();
@@ -91,17 +91,17 @@ describe('ReadyToMerge', () => {
   });
 
   describe('computed', () => {
-    describe('shouldShowMergeWhenPipelineSucceedsText', () => {
+    describe('shouldShowAutoMergeText', () => {
       it('should return true with active pipeline', () => {
         vm.mr.isPipelineActive = true;
 
-        expect(vm.shouldShowMergeWhenPipelineSucceedsText).toBeTruthy();
+        expect(vm.shouldShowAutoMergeText).toBeTruthy();
       });
 
       it('should return false with inactive pipeline', () => {
         vm.mr.isPipelineActive = false;
 
-        expect(vm.shouldShowMergeWhenPipelineSucceedsText).toBeFalsy();
+        expect(vm.shouldShowAutoMergeText).toBeFalsy();
       });
     });
 
@@ -325,16 +325,20 @@ describe('ReadyToMerge', () => {
         vm.handleMergeButtonClick(true);
 
         setTimeout(() => {
-          expect(vm.setToMergeWhenPipelineSucceeds).toBeTruthy();
+          expect(vm.autoMergeStrategy).toBe('merge_when_pipeline_succeeds');
           expect(vm.isMakingRequest).toBeTruthy();
           expect(eventHub.$emit).toHaveBeenCalledWith('MRWidgetUpdateRequested');
 
           const params = vm.service.merge.calls.argsFor(0)[0];
 
-          expect(params.sha).toEqual(vm.mr.sha);
-          expect(params.commit_message).toEqual(vm.mr.commitMessage);
-          expect(params.should_remove_source_branch).toBeFalsy();
-          expect(params.merge_when_pipeline_succeeds).toBeTruthy();
+          expect(params).toEqual(
+            jasmine.objectContaining({
+              sha: vm.mr.sha,
+              commit_message: vm.mr.commitMessage,
+              should_remove_source_branch: false,
+              auto_merge_strategy: 'merge_when_pipeline_succeeds',
+            }),
+          );
           done();
         }, 333);
       });
@@ -345,7 +349,7 @@ describe('ReadyToMerge', () => {
         vm.handleMergeButtonClick(false, true);
 
         setTimeout(() => {
-          expect(vm.setToMergeWhenPipelineSucceeds).toBeFalsy();
+          expect(vm.autoMergeStrategy).toBeUndefined();
           expect(vm.isMakingRequest).toBeTruthy();
           expect(eventHub.$emit).toHaveBeenCalledWith('FailedToMerge', undefined);
 
@@ -363,7 +367,7 @@ describe('ReadyToMerge', () => {
         vm.handleMergeButtonClick();
 
         setTimeout(() => {
-          expect(vm.setToMergeWhenPipelineSucceeds).toBeFalsy();
+          expect(vm.autoMergeStrategy).toBeUndefined();
           expect(vm.isMakingRequest).toBeTruthy();
           expect(vm.initiateMergePolling).toHaveBeenCalled();
 
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index c72b6e9033d..43c61c48fe5 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -1038,14 +1038,28 @@ describe MergeRequest do
     end
   end
 
-  describe "#reset_merge_when_pipeline_succeeds" do
+  describe "#auto_merge_strategy" do
+    subject { merge_request.auto_merge_strategy }
+
+    let(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+    it { is_expected.to eq('merge_when_pipeline_succeeds') }
+
+    context 'when auto merge is disabled' do
+      let(:merge_request) { create(:merge_request) }
+
+      it { is_expected.to be_nil }
+    end
+  end
+
+  describe "#reset_auto_merge" do
     let(:merge_if_green) do
       create :merge_request, merge_when_pipeline_succeeds: true, merge_user: create(:user),
                              merge_params: { "should_remove_source_branch" => "1", "commit_message" => "msg" }
     end
 
     it "sets the item to false" do
-      merge_if_green.reset_merge_when_pipeline_succeeds
+      merge_if_green.reset_auto_merge
       merge_if_green.reload
 
       expect(merge_if_green.merge_when_pipeline_succeeds).to be_falsey
diff --git a/spec/presenters/merge_request_presenter_spec.rb b/spec/presenters/merge_request_presenter_spec.rb
index 0e1aed42cc5..6408b0bd748 100644
--- a/spec/presenters/merge_request_presenter_spec.rb
+++ b/spec/presenters/merge_request_presenter_spec.rb
@@ -207,25 +207,25 @@ describe MergeRequestPresenter do
     end
   end
 
-  describe '#cancel_merge_when_pipeline_succeeds_path' do
+  describe '#cancel_auto_merge_path' do
     subject do
       described_class.new(resource, current_user: user)
-        .cancel_merge_when_pipeline_succeeds_path
+        .cancel_auto_merge_path
     end
 
     context 'when can cancel mwps' do
       it 'returns path' do
-        allow(resource).to receive(:can_cancel_merge_when_pipeline_succeeds?)
+        allow(resource).to receive(:can_cancel_auto_merge?)
           .with(user)
           .and_return(true)
 
-        is_expected.to eq("/#{resource.project.full_path}/merge_requests/#{resource.iid}/cancel_merge_when_pipeline_succeeds")
+        is_expected.to eq("/#{resource.project.full_path}/merge_requests/#{resource.iid}/cancel_auto_merge")
       end
     end
 
     context 'when cannot cancel mwps' do
       it 'returns nil' do
-        allow(resource).to receive(:can_cancel_merge_when_pipeline_succeeds?)
+        allow(resource).to receive(:can_cancel_auto_merge?)
           .with(user)
           .and_return(false)
 
diff --git a/spec/requests/api/merge_requests_spec.rb b/spec/requests/api/merge_requests_spec.rb
index 5c94a87529b..9f9180bc8c9 100644
--- a/spec/requests/api/merge_requests_spec.rb
+++ b/spec/requests/api/merge_requests_spec.rb
@@ -1473,7 +1473,7 @@ describe API::MergeRequests do
     end
 
     it "enables merge when pipeline succeeds if the pipeline is active" do
-      allow_any_instance_of(MergeRequest).to receive(:head_pipeline).and_return(pipeline)
+      allow_any_instance_of(MergeRequest).to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
       allow(pipeline).to receive(:active?).and_return(true)
 
       put api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/merge", user), params: { merge_when_pipeline_succeeds: true }
@@ -1484,7 +1484,7 @@ describe API::MergeRequests do
     end
 
     it "enables merge when pipeline succeeds if the pipeline is active and only_allow_merge_if_pipeline_succeeds is true" do
-      allow_any_instance_of(MergeRequest).to receive(:head_pipeline).and_return(pipeline)
+      allow_any_instance_of(MergeRequest).to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
       allow(pipeline).to receive(:active?).and_return(true)
       project.update_attribute(:only_allow_merge_if_pipeline_succeeds, true)
 
@@ -1950,7 +1950,7 @@ describe API::MergeRequests do
 
   describe 'POST :id/merge_requests/:merge_request_iid/cancel_merge_when_pipeline_succeeds' do
     before do
-      ::MergeRequests::MergeWhenPipelineSucceedsService.new(merge_request.target_project, user).execute(merge_request)
+      ::AutoMergeService.new(merge_request.target_project, user).execute(merge_request, AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
     end
 
     it 'removes the merge_when_pipeline_succeeds status' do
diff --git a/spec/serializers/merge_request_widget_entity_spec.rb b/spec/serializers/merge_request_widget_entity_spec.rb
index b89898f26f7..a27c22191f4 100644
--- a/spec/serializers/merge_request_widget_entity_spec.rb
+++ b/spec/serializers/merge_request_widget_entity_spec.rb
@@ -297,4 +297,50 @@ describe MergeRequestWidgetEntity do
       end
     end
   end
+
+  describe 'auto merge' do
+    context 'when auto merge is enabled' do
+      let(:resource) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+      it 'returns auto merge related information' do
+        expect(subject[:auto_merge_enabled]).to be_truthy
+        expect(subject[:auto_merge_strategy]).to eq('merge_when_pipeline_succeeds')
+      end
+    end
+
+    context 'when auto merge is not enabled' do
+      let(:resource) { create(:merge_request) }
+
+      it 'returns auto merge related information' do
+        expect(subject[:auto_merge_enabled]).to be_falsy
+        expect(subject[:auto_merge_strategy]).to be_nil
+      end
+    end
+
+    context 'when head pipeline is running' do
+      before do
+        create(:ci_pipeline, :running, project: project,
+                                       ref: resource.source_branch,
+                                       sha: resource.diff_head_sha)
+        resource.update_head_pipeline
+      end
+
+      it 'returns available auto merge strategies' do
+        expect(subject[:available_auto_merge_strategies]).to eq(%w[merge_when_pipeline_succeeds])
+      end
+    end
+
+    context 'when head pipeline is finished' do
+      before do
+        create(:ci_pipeline, :success, project: project,
+                                       ref: resource.source_branch,
+                                       sha: resource.diff_head_sha)
+        resource.update_head_pipeline
+      end
+
+      it 'returns available auto merge strategies' do
+        expect(subject[:available_auto_merge_strategies]).to be_empty
+      end
+    end
+  end
 end
diff --git a/spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb b/spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb
index 96f61f3f103..a20bf8e17e4 100644
--- a/spec/services/merge_requests/merge_when_pipeline_succeeds_service_spec.rb
+++ b/spec/services/auto_merge/merge_when_pipeline_succeeds_service_spec.rb
@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-describe MergeRequests::MergeWhenPipelineSucceedsService do
+describe AutoMerge::MergeWhenPipelineSucceedsService do
   let(:user) { create(:user) }
   let(:project) { create(:project, :repository) }
 
@@ -21,6 +21,27 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
     described_class.new(project, user, commit_message: 'Awesome message')
   end
 
+  describe "#available_for?" do
+    subject { service.available_for?(mr_merge_if_green_enabled) }
+
+    let(:pipeline_status) { :running }
+
+    before do
+      create(:ci_pipeline, pipeline_status, ref: mr_merge_if_green_enabled.source_branch,
+                                            sha: mr_merge_if_green_enabled.diff_head_sha,
+                                            project: mr_merge_if_green_enabled.source_project)
+      mr_merge_if_green_enabled.update_head_pipeline
+    end
+
+    it { is_expected.to be_truthy }
+
+    context 'when the head piipeline succeeded' do
+      let(:pipeline_status) { :success }
+
+      it { is_expected.to be_falsy }
+    end
+  end
+
   describe "#execute" do
     let(:merge_request) do
       create(:merge_request, target_project: project, source_project: project,
@@ -30,8 +51,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
     context 'first time enabling' do
       before do
         allow(merge_request)
-          .to receive(:head_pipeline)
-          .and_return(pipeline)
+          .to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
 
         service.execute(merge_request)
       end
@@ -39,7 +59,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       it 'sets the params, merge_user, and flag' do
         expect(merge_request).to be_valid
         expect(merge_request.merge_when_pipeline_succeeds).to be_truthy
-        expect(merge_request.merge_params).to eq commit_message: 'Awesome message'
+        expect(merge_request.merge_params).to include commit_message: 'Awesome message'
         expect(merge_request.merge_user).to be user
       end
 
@@ -54,8 +74,8 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       let(:build)   { create(:ci_build, ref: mr_merge_if_green_enabled.source_branch) }
 
       before do
-        allow(mr_merge_if_green_enabled).to receive(:head_pipeline)
-          .and_return(pipeline)
+        allow(mr_merge_if_green_enabled)
+          .to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
 
         allow(mr_merge_if_green_enabled).to receive(:mergeable?)
           .and_return(true)
@@ -72,7 +92,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
     end
   end
 
-  describe "#trigger" do
+  describe "#process" do
     let(:merge_request_ref) { mr_merge_if_green_enabled.source_branch }
     let(:merge_request_head) do
       project.commit(mr_merge_if_green_enabled.source_branch).id
@@ -86,8 +106,11 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       end
 
       it "merges all merge requests with merge when the pipeline succeeds enabled" do
+        allow(mr_merge_if_green_enabled)
+          .to receive_messages(head_pipeline: triggering_pipeline, actual_head_pipeline: triggering_pipeline)
+
         expect(MergeWorker).to receive(:perform_async)
-        service.trigger(triggering_pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
 
@@ -99,7 +122,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
 
       it 'does not merge request' do
         expect(MergeWorker).not_to receive(:perform_async)
-        service.trigger(old_pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
 
@@ -111,7 +134,7 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
 
       it 'does not merge request' do
         expect(MergeWorker).not_to receive(:perform_async)
-        service.trigger(unrelated_pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
 
@@ -125,8 +148,11 @@ describe MergeRequests::MergeWhenPipelineSucceedsService do
       end
 
       it 'merges the associated merge request' do
+        allow(mr_merge_if_green_enabled)
+          .to receive_messages(head_pipeline: pipeline, actual_head_pipeline: pipeline)
+
         expect(MergeWorker).to receive(:perform_async)
-        service.trigger(pipeline)
+        service.process(mr_merge_if_green_enabled)
       end
     end
   end
diff --git a/spec/services/auto_merge_service_spec.rb b/spec/services/auto_merge_service_spec.rb
new file mode 100644
index 00000000000..d0eefed3150
--- /dev/null
+++ b/spec/services/auto_merge_service_spec.rb
@@ -0,0 +1,140 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe AutoMergeService do
+  set(:project) { create(:project) }
+  set(:user) { create(:user) }
+  let(:service) { described_class.new(project, user) }
+
+  describe '.all_strategies' do
+    subject { described_class.all_strategies }
+
+    it 'returns all strategies' do
+      is_expected.to eq(AutoMergeService::STRATEGIES)
+    end
+  end
+
+  describe '#available_strategies' do
+    subject { service.available_strategies(merge_request) }
+
+    let(:merge_request) { create(:merge_request) }
+    let(:pipeline_status) { :running }
+
+    before do
+      create(:ci_pipeline, pipeline_status, ref: merge_request.source_branch,
+                                            sha: merge_request.diff_head_sha,
+                                            project: merge_request.source_project)
+
+      merge_request.update_head_pipeline
+    end
+
+    it 'returns available strategies' do
+      is_expected.to include('merge_when_pipeline_succeeds')
+    end
+
+    context 'when the head piipeline succeeded' do
+      let(:pipeline_status) { :success }
+
+      it 'returns available strategies' do
+        is_expected.to be_empty
+      end
+    end
+  end
+
+  describe '.get_service_class' do
+    subject { described_class.get_service_class(strategy) }
+
+    let(:strategy) { AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS }
+
+    it 'returns service instance' do
+      is_expected.to eq(AutoMerge::MergeWhenPipelineSucceedsService)
+    end
+
+    context 'when strategy is not present' do
+      let(:strategy) { }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#execute' do
+    subject { service.execute(merge_request, strategy) }
+
+    let(:merge_request) { create(:merge_request) }
+    let(:pipeline_status) { :running }
+    let(:strategy) { AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS }
+
+    before do
+      create(:ci_pipeline, pipeline_status, ref: merge_request.source_branch,
+                                            sha: merge_request.diff_head_sha,
+                                            project: merge_request.source_project)
+
+      merge_request.update_head_pipeline
+    end
+
+    it 'delegates to a relevant service instance' do
+      expect_next_instance_of(AutoMerge::MergeWhenPipelineSucceedsService) do |service|
+        expect(service).to receive(:execute).with(merge_request)
+      end
+
+      subject
+    end
+
+    context 'when the head piipeline succeeded' do
+      let(:pipeline_status) { :success }
+
+      it 'returns failed' do
+        is_expected.to eq(:failed)
+      end
+    end
+  end
+
+  describe '#process' do
+    subject { service.process(merge_request) }
+
+    let(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+    it 'delegates to a relevant service instance' do
+      expect_next_instance_of(AutoMerge::MergeWhenPipelineSucceedsService) do |service|
+        expect(service).to receive(:process).with(merge_request)
+      end
+
+      subject
+    end
+
+    context 'when auto merge is not enabled' do
+      let(:merge_request) { create(:merge_request) }
+
+      it 'returns nil' do
+        is_expected.to be_nil
+      end
+    end
+  end
+
+  describe '#cancel' do
+    subject { service.cancel(merge_request) }
+
+    let(:merge_request) { create(:merge_request, :merge_when_pipeline_succeeds) }
+
+    it 'delegates to a relevant service instance' do
+      expect_next_instance_of(AutoMerge::MergeWhenPipelineSucceedsService) do |service|
+        expect(service).to receive(:cancel).with(merge_request)
+      end
+
+      subject
+    end
+
+    context 'when auto merge is not enabled' do
+      let(:merge_request) { create(:merge_request) }
+
+      it 'returns error' do
+        expect(subject[:message]).to eq("Can't cancel the automatic merge")
+        expect(subject[:status]).to eq(:error)
+        expect(subject[:http_status]).to eq(406)
+      end
+    end
+  end
+end
diff --git a/spec/services/merge_requests/push_options_handler_service_spec.rb b/spec/services/merge_requests/push_options_handler_service_spec.rb
index f7a39bb42d5..54b9c6dae38 100644
--- a/spec/services/merge_requests/push_options_handler_service_spec.rb
+++ b/spec/services/merge_requests/push_options_handler_service_spec.rb
@@ -76,10 +76,11 @@ describe MergeRequests::PushOptionsHandlerService do
   shared_examples_for 'a service that can set the merge request to merge when pipeline succeeds' do
     subject(:last_mr) { MergeRequest.last }
 
-    it 'sets merge_when_pipeline_succeeds' do
+    it 'sets auto_merge_enabled' do
       service.execute
 
-      expect(last_mr.merge_when_pipeline_succeeds).to eq(true)
+      expect(last_mr.auto_merge_enabled).to eq(true)
+      expect(last_mr.auto_merge_strategy).to eq(AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS)
     end
 
     it 'sets merge_user to the user' do
diff --git a/spec/services/merge_requests/refresh_service_spec.rb b/spec/services/merge_requests/refresh_service_spec.rb
index 7258428589f..6ba67c7165c 100644
--- a/spec/services/merge_requests/refresh_service_spec.rb
+++ b/spec/services/merge_requests/refresh_service_spec.rb
@@ -23,7 +23,8 @@ describe MergeRequests::RefreshService do
                               source_branch: 'master',
                               target_branch: 'feature',
                               target_project: @project,
-                              merge_when_pipeline_succeeds: true,
+                              auto_merge_enabled: true,
+                              auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
                               merge_user: @user)
 
       @another_merge_request = create(:merge_request,
@@ -31,7 +32,8 @@ describe MergeRequests::RefreshService do
                                       source_branch: 'master',
                                       target_branch: 'test',
                                       target_project: @project,
-                                      merge_when_pipeline_succeeds: true,
+                                      auto_merge_enabled: true,
+                                      auto_merge_strategy: AutoMergeService::STRATEGY_MERGE_WHEN_PIPELINE_SUCCEEDS,
                                       merge_user: @user)
 
       @fork_merge_request = create(:merge_request,
@@ -83,7 +85,7 @@ describe MergeRequests::RefreshService do
 
         expect(@merge_request.notes).not_to be_empty
         expect(@merge_request).to be_open
-        expect(@merge_request.merge_when_pipeline_succeeds).to be_falsey
+        expect(@merge_request.auto_merge_enabled).to be_falsey
         expect(@merge_request.diff_head_sha).to eq(@newrev)
         expect(@fork_merge_request).to be_open
         expect(@fork_merge_request.notes).to be_empty
@@ -292,7 +294,7 @@ describe MergeRequests::RefreshService do
 
         expect(@merge_request.notes).not_to be_empty
         expect(@merge_request).to be_open
-        expect(@merge_request.merge_when_pipeline_succeeds).to be_falsey
+        expect(@merge_request.auto_merge_enabled).to be_falsey
         expect(@merge_request.diff_head_sha).to eq(@newrev)
         expect(@fork_merge_request).to be_open
         expect(@fork_merge_request.notes).to be_empty
diff --git a/spec/services/merge_requests/update_service_spec.rb b/spec/services/merge_requests/update_service_spec.rb
index ba4c9ce60f3..fbfcd95e204 100644
--- a/spec/services/merge_requests/update_service_spec.rb
+++ b/spec/services/merge_requests/update_service_spec.rb
@@ -217,8 +217,9 @@ describe MergeRequests::UpdateService, :mailer do
             head_pipeline_of: merge_request
           )
 
-          expect(MergeRequests::MergeWhenPipelineSucceedsService).to receive(:new).with(project, user)
+          expect(AutoMerge::MergeWhenPipelineSucceedsService).to receive(:new).with(project, user, {})
             .and_return(service_mock)
+          allow(service_mock).to receive(:available_for?) { true }
           expect(service_mock).to receive(:execute).with(merge_request)
         end
 
diff --git a/spec/workers/pipeline_success_worker_spec.rb b/spec/workers/pipeline_success_worker_spec.rb
index 4cbe384b47a..b511edfa620 100644
--- a/spec/workers/pipeline_success_worker_spec.rb
+++ b/spec/workers/pipeline_success_worker_spec.rb
@@ -5,12 +5,13 @@ require 'spec_helper'
 describe PipelineSuccessWorker do
   describe '#perform' do
     context 'when pipeline exists' do
-      let(:pipeline) { create(:ci_pipeline, status: 'success') }
+      let(:pipeline) { create(:ci_pipeline, status: 'success', ref: merge_request.source_branch, project: merge_request.source_project) }
+      let(:merge_request) { create(:merge_request) }
 
       it 'performs "merge when pipeline succeeds"' do
-        expect_any_instance_of(
-          MergeRequests::MergeWhenPipelineSucceedsService
-        ).to receive(:trigger)
+        expect_next_instance_of(AutoMergeService) do |auto_merge|
+          expect(auto_merge).to receive(:process)
+        end
 
         described_class.new.perform(pipeline.id)
       end