Add a test for checking validates :key does not override by concern

spec/models/ci/variable_spec.rb

@@ -6,6 +6,40 @@ describe Ci::Variable, models: true do
   it { is_expected.to be_kind_of(HasVariable) }
   it { is_expected.to validate_uniqueness_of(:key).scoped_to(:project_id) }
 
+  describe 'validates :key' do
+    let(:project) { create(:project) }
+
+    it 'be invalid if it exceeds maximum' do
+      expect do
+        create(:ci_variable, project: project, key: "A"*256)
+      end.to raise_error(ActiveRecord::RecordInvalid)
+    end
+
+    it 'be invalid if violates constraints' do
+      expect do
+        create(:ci_variable, project: project, key: "*")
+      end.to raise_error(ActiveRecord::RecordInvalid)
+    end
+
+    context 'when there is a variable' do
+      before do
+        create(:ci_variable, key: 'AAA', project: project)
+      end
+
+      it 'be valid if it is unique' do
+        expect do
+          create(:ci_variable, project: project, key: 'CCC')
+        end.not_to raise_error
+      end
+
+      it 'be invalid if it is duplicated' do
+        expect do
+          create(:ci_variable, project: project, key: 'AAA')
+        end.to raise_error(ActiveRecord::RecordInvalid)
+      end
+    end
+  end
+
   describe '.unprotected' do
     subject { described_class.unprotected }