diff --git a/test/string_calculator_test.dart b/test/string_calculator_test.dart
index d48b197..d47aa8b 100644
--- a/test/string_calculator_test.dart
+++ b/test/string_calculator_test.dart
@@ -12,5 +12,10 @@ void main() {
     test('empty string returns 0', () {
       expect(calculator.add(''), equals(0));
     });
+
+    test('single number returns that number', () {
+      expect(calculator.add('5'), equals(5));
+      expect(calculator.add('42'), equals(42));
+    });
   });
 }