Unique environment scope for group clusters

We allow setting of environment scopes in EE. Add validations for group
clusters.

ee/app/models/ee/clusters/cluster.rb

@@ -15,6 +15,11 @@ module EE
           return false
         end
 
+        if group && group.clusters.where(environment_scope: environment_scope).where.not(id: self.id).exists?
+          errors.add(:base, 'cannot add duplicated environment scope')
+          return false
+        end
+
         true
       end
     end

ee/spec/models/ee/clusters/cluster_spec.rb

@@ -7,6 +7,7 @@ describe Clusters::Cluster do
     subject { cluster.valid? }
 
     context 'when validates unique_environment_scope' do
+      context 'for a project cluster' do
         let(:project) { create(:project) }
 
         before do
@@ -32,5 +33,32 @@ describe Clusters::Cluster do
           it { is_expected.to be_truthy }
         end
       end
+
+      context 'for a group cluster' do
+        let(:group) { create(:group) }
+
+        before do
+          create(:cluster, cluster_type: :group_type, groups: [group], environment_scope: 'product/*')
+        end
+
+        context 'when identical environment scope exists in group' do
+          let(:cluster) { build(:cluster, cluster_type: :group_type, groups: [group], environment_scope: 'product/*') }
+
+          it { is_expected.to be_falsey }
+        end
+
+        context 'when identical environment scope does not exist in group' do
+          let(:cluster) { build(:cluster, cluster_type: :group_type, groups: [group], environment_scope: '*') }
+
+          it { is_expected.to be_truthy }
+        end
+
+        context 'when identical environment scope exists in different group' do
+          let(:cluster) { build(:cluster, :group, environment_scope: 'product/*') }
+
+          it { is_expected.to be_truthy }
+        end
+      end
+    end
   end
 end