Add test for Project#protected_for?

spec/models/project_spec.rb

@@ -1796,6 +1796,43 @@ describe Project, models: true do
     end
   end
 
+  describe '#protected_for?' do
+    let(:project) { create(:empty_project) }
+
+    subject { project.protected_for?('ref') }
+
+    context 'when the ref is not protected' do
+      before do
+        stub_application_setting(
+          default_branch_protection: Gitlab::Access::PROTECTION_NONE)
+      end
+
+      it 'returns false' do
+        is_expected.to be_falsey
+      end
+    end
+
+    context 'when the ref is a protected branch' do
+      before do
+        create(:protected_branch, name: 'ref', project: project)
+      end
+
+      it 'returns true' do
+        is_expected.to be_truthy
+      end
+    end
+
+    context 'when the ref is a protected tag' do
+      before do
+        create(:protected_tag, name: 'ref', project: project)
+      end
+
+      it 'returns true' do
+        is_expected.to be_truthy
+      end
+    end
+  end
+
   describe '#update_project_statistics' do
     let(:project) { create(:empty_project) }