added counter

spec/models/supporter_spec.rb

@@ -10,4 +10,16 @@ describe Supporter do
   it { is_expected.to validate_uniqueness_of(:email) }
   it { is_expected.to validate_presence_of(:support) }
   it { is_expected.to validate_presence_of(:age_category) }
+
+  describe '.counter' do
+    it 'counts only from a certain number on' do
+      allow(Supporter).to receive(:count)  { 12 }
+
+      expect(Supporter.counter).to eq Supporter::COUNTER_START
+
+      allow(Supporter).to receive(:count)  { Supporter::COUNTER_START + 12 }
+
+      expect(Supporter.counter).to eq Supporter::COUNTER_START + 12
+    end
+  end
 end