Add MR validation spec

spec/models/merge_request_spec.rb

@@ -221,6 +221,59 @@
         expect(subject).to be_valid
       end
     end
+
+    context 'for collaboration' do
+      let(:project) { create(:project, :public, merge_requests_require_allow_collaboration: true) }
+      let(:fork) { fork_project(project) }
+      let(:can_push) { true }
+      let(:is_protected) { false }
+
+      before do
+        allow(subject).to receive(:can_push_to_source_project?).and_return(can_push)
+        allow(subject).to receive(:protected_source_branch?).and_return(is_protected)
+        subject.source_project = source_project
+        subject.target_project = target_project
+      end
+
+      context 'when source and target project are the same' do
+        let(:target_project) { project }
+        let(:source_project) { project }
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'when source and target project are different' do
+        let(:target_project) { project }
+        let(:source_project) { fork }
+
+        it { is_expected.to be_valid }
+      end
+
+      context 'when source branch is protected' do
+        let(:target_project) { project }
+        let(:source_project) { fork }
+        let(:is_protected) { true }
+
+        it { is_expected.not_to be_valid }
+      end
+
+      context 'when author cannot push code to source project' do
+        let(:target_project) { project }
+        let(:source_project) { fork }
+        let(:can_push) { false }
+
+        it { is_expected.not_to be_valid }
+      end
+
+      context 'when author cannot allow collaboration but project does not require it' do
+        let(:project) { create(:project, :public) }
+        let(:target_project) { project }
+        let(:source_project) { fork }
+        let(:is_protected) { true }
+
+        it { is_expected.to be_valid }
+      end
+    end
   end
 
   describe 'callbacks' do