1 files changed, 187 insertions, 0 deletions
diff --git a/spec/services/merge_requests/mergeability_check_service_spec.rb b/spec/services/merge_requests/mergeability_check_service_spec.rb
new file mode 100644
index 00000000000..aa0485467ed
--- /dev/null
+++ b/spec/services/merge_requests/mergeability_check_service_spec.rb
@@ -0,0 +1,187 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe MergeRequests::MergeabilityCheckService do
+  shared_examples_for 'unmergeable merge request' do
+    it 'updates or keeps merge status as cannot_be_merged' do
+      subject
+
+      expect(merge_request.merge_status).to eq('cannot_be_merged')
+    end
+
+    it 'does not change the merge ref HEAD' do
+      expect { subject }.not_to change(merge_request, :merge_ref_head)
+    end
+
+    it 'returns ServiceResponse.error' do
+      result = subject
+
+      expect(result).to be_a(ServiceResponse)
+      expect(result).to be_error
+    end
+  end
+
+  shared_examples_for 'mergeable merge request' do
+    it 'updates or keeps merge status as can_be_merged' do
+      subject
+
+      expect(merge_request.merge_status).to eq('can_be_merged')
+    end
+
+    it 'updates the merge ref' do
+      expect { subject }.to change(merge_request, :merge_ref_head).from(nil)
+    end
+
+    it 'returns ServiceResponse.success' do
+      result = subject
+
+      expect(result).to be_a(ServiceResponse)
+      expect(result).to be_success
+    end
+
+    it 'ServiceResponse has merge_ref_head payload' do
+      result = subject
+
+      expect(result.payload.keys).to contain_exactly(:merge_ref_head)
+      expect(result.payload[:merge_ref_head].keys)
+        .to contain_exactly(:commit_id, :target_id, :source_id)
+    end
+  end
+
+  describe '#execute' do
+    let(:project) { create(:project, :repository) }
+    let(:merge_request) { create(:merge_request, merge_status: :unchecked, source_project: project, target_project: project) }
+    let(:repo) { project.repository }
+
+    subject { described_class.new(merge_request).execute }
+
+    before do
+      project.add_developer(merge_request.author)
+    end
+
+    it_behaves_like 'mergeable merge request'
+
+    context 'when multiple calls to the service' do
+      it 'returns success' do
+        subject
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.success?).to be(true)
+      end
+
+      it 'second call does not change the merge-ref' do
+        expect { subject }.to change(merge_request, :merge_ref_head).from(nil)
+        expect { subject }.not_to change(merge_request, :merge_ref_head)
+      end
+    end
+
+    context 'when broken' do
+      before do
+        allow(merge_request).to receive(:broken?) { true }
+        allow(project.repository).to receive(:can_be_merged?) { false }
+      end
+
+      it_behaves_like 'unmergeable merge request'
+
+      it 'returns ServiceResponse.error' do
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.error?).to be(true)
+        expect(result.message).to eq('Merge request is not mergeable')
+      end
+    end
+
+    context 'when it has conflicts' do
+      before do
+        allow(merge_request).to receive(:broken?) { false }
+        allow(project.repository).to receive(:can_be_merged?) { false }
+      end
+
+      it_behaves_like 'unmergeable merge request'
+
+      it 'returns ServiceResponse.error' do
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.error?).to be(true)
+        expect(result.message).to eq('Merge request is not mergeable')
+      end
+    end
+
+    context 'when MR cannot be merged and has no merge ref' do
+      before do
+        merge_request.mark_as_unmergeable!
+      end
+
+      it_behaves_like 'unmergeable merge request'
+
+      it 'returns ServiceResponse.error' do
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.error?).to be(true)
+        expect(result.message).to eq('Merge request is not mergeable')
+      end
+    end
+
+    context 'when MR cannot be merged and has outdated merge ref' do
+      before do
+        MergeRequests::MergeToRefService.new(project, merge_request.author).execute(merge_request)
+        merge_request.mark_as_unmergeable!
+      end
+
+      it_behaves_like 'unmergeable merge request'
+
+      it 'returns ServiceResponse.error' do
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.error?).to be(true)
+        expect(result.message).to eq('Merge request is not mergeable')
+      end
+    end
+
+    context 'when merge request is not given' do
+      subject { described_class.new(nil).execute }
+
+      it 'returns ServiceResponse.error' do
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.message).to eq('Invalid argument')
+      end
+    end
+
+    context 'when read only DB' do
+      it 'returns ServiceResponse.error' do
+        allow(Gitlab::Database).to receive(:read_only?) { true }
+
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.message).to eq('Unsupported operation')
+      end
+    end
+
+    context 'when MR is mergeable but merge-ref does not exists' do
+      before do
+        merge_request.mark_as_mergeable!
+      end
+
+      it 'keeps merge status as can_be_merged' do
+        expect { subject }.not_to change(merge_request, :merge_status).from('can_be_merged')
+      end
+
+      it 'returns ServiceResponse.error' do
+        result = subject
+
+        expect(result).to be_a(ServiceResponse)
+        expect(result.error?).to be(true)
+        expect(result.message).to eq('Merge ref was not found')
+      end
+    end
+  end
+end