Add negative example with duplicate variable in spec

spec/ee/spec/controllers/ee/projects/variables_controller_spec.rb

@@ -13,9 +13,23 @@ describe Projects::VariablesController do
   end
 
   describe 'PATCH #update' do
-    let!(:variable) { create(:ci_variable, project: project) }
+    let!(:variable) { create(:ci_variable, project: project, environment_scope: 'custom_scope') }
     let(:owner) { project }
 
+    let(:variable_attributes) do
+      { id: variable.id,
+        key: variable.key,
+        value: variable.value,
+        protected: variable.protected?.to_s,
+        environment_scope: variable.environment_scope }
+    end
+    let(:new_variable_attributes) do
+      { key: 'new_key',
+        value: 'dummy_value',
+        protected: 'false',
+        environment_scope: 'new_scope' }
+    end
+
     subject do
       patch :update,
         namespace_id: project.namespace.to_param,
@@ -25,23 +39,10 @@ describe Projects::VariablesController do
     end
 
     context 'with same key and different environment scope' do
-      let(:variable_attributes) do
-        { id: variable.id,
-          key: variable.key,
-          value: variable.value,
-          protected: variable.protected?.to_s,
-          environment_scope: variable.environment_scope }
-      end
-      let(:new_variable_attributes) do
-        { key: variable.key,
-          value: 'dummy_value',
-          protected: 'false',
-          environment_scope: 'prod' }
-      end
       let(:variables_attributes) do
         [
           variable_attributes,
-          new_variable_attributes
+          new_variable_attributes.merge(key: variable.key)
         ]
       end
 
@@ -65,5 +66,28 @@ describe Projects::VariablesController do
         expect(response).to match_response_schema('variables')
       end
     end
+
+    context 'with same key and same environment scope' do
+      let(:variables_attributes) do
+        [
+          variable_attributes,
+          new_variable_attributes.merge(key: variable.key, environment_scope: variable.environment_scope)
+        ]
+      end
+
+      it 'does not update the existing variable' do
+        expect { subject }.not_to change { variable.reload.value }
+      end
+
+      it 'does not create the new variable' do
+        expect { subject }.not_to change { owner.variables.count }
+      end
+
+      it 'returns a bad request response' do
+        subject
+
+        expect(response).to have_gitlab_http_status(:bad_request)
+      end
+    end
   end
 end