Add specs to auth helper

spec/helpers/auth_helper_spec.rb

@@ -154,4 +154,34 @@ describe AuthHelper do
       expect(helper.unlink_provider_allowed?(provider)).to eq 'policy_unlink_result'
     end
   end
+
+  describe '#provider_has_icon?' do
+    it 'returns true for defined providers' do
+      expect(helper.provider_has_icon?(described_class::PROVIDERS_WITH_ICONS.sample)).to eq true
+    end
+
+    it 'returns false for undefined providers' do
+      expect(helper.provider_has_icon?('test')).to be_falsey
+    end
+
+    context 'when provider is defined by config' do
+      before do
+        allow(Gitlab::Auth::OAuth::Provider).to receive(:icon_for).with('test').and_return('icon')
+      end
+
+      it 'returns true' do
+        expect(helper.provider_has_icon?('test')).to be_truthy
+      end
+    end
+
+    context 'when provider is not defined by config' do
+      before do
+        allow(Gitlab::Auth::OAuth::Provider).to receive(:icon_for).with('test').and_return(nil)
+      end
+
+      it 'returns true' do
+        expect(helper.provider_has_icon?('test')).to be_falsey
+      end
+    end
+  end
 end