Make nonce-only payment sources non-reusable

app/models/solidus_paypal_braintree/source.rb

@@ -67,7 +67,7 @@ def paypal?
     end
 
     def reusable?
-      true
+      token.present?
     end
 
     def credit_card?

spec/models/solidus_paypal_braintree/source_spec.rb

@@ -332,4 +332,20 @@
       it { is_expected.to be_nil }
     end
   end
+
+  describe '#reusable?' do
+    let(:payment_source) { described_class.new(token: token, nonce: nonce) }
+    let(:nonce) { 'nonce67890' }
+    subject { payment_source.reusable? }
+
+    context 'when source token is present' do
+      let(:token) { 'token12345' }
+      it { is_expected.to be_truthy }
+    end
+
+    context 'when source token is nil' do
+      let(:token) { nil }
+      it { is_expected.to be_falsy }
+    end
+  end
 end