use #described_class, as suggested by RuboCop

spec/lib/nonce_store_spec.rb

@@ -6,36 +6,36 @@ describe NonceStore do
   describe '.add' do
     it 'stores a nonce in the cache' do
       expect(Rails.cache).to receive(:write)
-      NonceStore.add(nonce)
+      described_class.add(nonce)
     end
   end
 
   describe '.delete' do
     it 'deletes a nonce from the cache' do
       expect(Rails.cache).to receive(:write)
-      NonceStore.add(nonce)
-      NonceStore.delete(nonce)
-      expect(NonceStore.has?(nonce)).to be false
+      described_class.add(nonce)
+      described_class.delete(nonce)
+      expect(described_class.has?(nonce)).to be false
     end
   end
 
   describe '.has?' do
     it 'returns true for present nonces' do
-      NonceStore.add(nonce)
-      expect(NonceStore.has?(nonce)).to be true
+      described_class.add(nonce)
+      expect(described_class.has?(nonce)).to be true
     end
 
     it 'returns false for expired nonces' do
       Lti.send(:remove_const, 'MAXIMUM_SESSION_AGE')
       Lti::MAXIMUM_SESSION_AGE = 1
-      NonceStore.add(nonce)
-      expect(NonceStore.has?(nonce)).to be true
+      described_class.add(nonce)
+      expect(described_class.has?(nonce)).to be true
       sleep(Lti::MAXIMUM_SESSION_AGE)
-      expect(NonceStore.has?(nonce)).to be false
+      expect(described_class.has?(nonce)).to be false
     end
 
     it 'returns false for absent nonces' do
-      expect(NonceStore.has?(nonce)).to be false
+      expect(described_class.has?(nonce)).to be false
     end
   end
 end