Merge branch 'feature/improve-mrwbs-and-todos-for-pipelines' into 'master'

Trigger Merge When Pipeline Succeeds on pipeline event

## What does this MR do?

This MR is meant to improve merge when build succeeds triggers, which has an impact on performance.

- [x] Move Merge When Build Succeeds trigger from commit status to pipeline event
- [x] Drop support for triggering event for branches that include commit status submitted without branch (no longer relevant)
- [x] Perform Merge When Pipeline Succeeds asynchronously to improve performance and avoid race conditions
- [x] Add missing feature test that verifies if MWBS feature actually works and merges merge requests
- [x] Update the documentation to reflect change in the behavior

Moved to separate merge request:

- [ ] Rename Merge When Build Succeeds to Merge When Pipeline Succeeds
- [ ] Update documentation to reflect name change for this feature

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [x] All builds are passing

See merge request !6675

1 files changed, 22 insertions, 0 deletions

diff --git a/spec/workers/pipeline_proccess_worker_spec.rb b/spec/workers/pipeline_proccess_worker_spec.rb
new file mode 100644
index 00000000000..86e9d7f6684
--- /dev/null
+++ b/spec/workers/pipeline_proccess_worker_spec.rb
@@ -0,0 +1,22 @@
+require 'spec_helper'
+
+describe PipelineProcessWorker do
+  describe '#perform' do
+    context 'when pipeline exists' do
+      let(:pipeline) { create(:ci_pipeline) }
+
+      it 'processes pipeline' do
+        expect_any_instance_of(Ci::Pipeline).to receive(:process!)
+
+        described_class.new.perform(pipeline.id)
+      end
+    end
+
+    context 'when pipeline does not exist' do
+      it 'does not raise exception' do
+        expect { described_class.new.perform(123) }
+          .not_to raise_error
+      end
+    end
+  end
+end