diff --git a/README.md b/README.md
index 656a696..23f655f 100644
--- a/README.md
+++ b/README.md
@@ -22,6 +22,8 @@ Calculator - [Caster.IO](https://caster.io) project to showcase testing techniqu
 
 [Lesson 9: Sharing code between tests with setUp() and tearDown()](https://caster.io/lessons/lesson-9-sharing-code-between-tests-with-setup-and-teardown) 👉🏾 [Branch](https://github.com/samuelematias/calculator_app/tree/lesson9)
 
+[Lesson 10: Testing Futures](https://caster.io/lessons/lesson-10-testing-futures) 👉🏾 [Branch](https://github.com/samuelematias/calculator_app/tree/lesson10)
+
 ## License
 
 ```
diff --git a/packages/calculator/lib/src/calculator.dart b/packages/calculator/lib/src/calculator.dart
index 45ec48d..bb5e065 100644
--- a/packages/calculator/lib/src/calculator.dart
+++ b/packages/calculator/lib/src/calculator.dart
@@ -10,4 +10,7 @@ class Calculator {
     if (b == 0) throw ArgumentError('You cannot divide by zero');
     return a / b;
   }
+
+  Future<double> powerOfTwo(double a) =>
+      Future.delayed(const Duration(seconds: 1), () => a * a);
 }
diff --git a/packages/calculator/test/calculator_test.dart b/packages/calculator/test/calculator_test.dart
index 171ebdb..3e97738 100644
--- a/packages/calculator/test/calculator_test.dart
+++ b/packages/calculator/test/calculator_test.dart
@@ -8,47 +8,55 @@ void main() {
     calculator = Calculator();
   });
 
-  group('add', () {
-    test('the calculator returns 4 when adding 2 and 2', () {
-      expect(calculator.add(2, 2), 4);
-    });
+  group('Calculator', () {
+    group('add', () {
+      test('returns 4 when adding 2 and 2', () {
+        expect(calculator.add(2, 2), 4);
+      });
 
-    test('the calculator returns 40 when adding 20 and 20', () {
-      expect(calculator.add(20, 20), 40);
+      test('returns 40 when adding 20 and 20', () {
+        expect(calculator.add(20, 20), 40);
+      });
     });
-  });
 
-  group('substract', () {
-    test('the calculator returns 10 when substracting 10 to 20', () {
-      expect(calculator.substract(20, 10), 10);
-    });
+    group('substract', () {
+      test('returns 10 when substracting 10 to 20', () {
+        expect(calculator.substract(20, 10), 10);
+      });
 
-    test('the calculator returns -4 when substracting 8 to 4', () {
-      expect(calculator.substract(4, 8), -4);
+      test('returns -4 when substracting 8 to 4', () {
+        expect(calculator.substract(4, 8), -4);
+      });
     });
-  });
 
-  group('multiple', () {
-    test('the calculator returns 45 when multiplying 5 tby 9', () {
-      expect(calculator.multiply(5, 9), 45);
-    });
+    group('multiple', () {
+      test('returns 45 when multiplying 5 tby 9', () {
+        expect(calculator.multiply(5, 9), 45);
+      });
 
-    test('the calculator returns 18 when multiplying 25 tby 9', () {
-      expect(calculator.multiply(2, 9), 18);
+      test('returns 18 when multiplying 25 tby 9', () {
+        expect(calculator.multiply(2, 9), 18);
+      });
     });
-  });
 
-  group('divide', () {
-    test('the calculator returns 9 when dividing 27 by 3', () {
-      expect(calculator.divide(27, 3), 9);
-    });
+    group('divide', () {
+      test('returns 9 when dividing 27 by 3', () {
+        expect(calculator.divide(27, 3), 9);
+      });
+
+      test('returns 1 when dividing 27 by 27', () {
+        expect(calculator.divide(27, 27), 1);
+      });
 
-    test('the calculator returns 1 when dividing 27 by 27', () {
-      expect(calculator.divide(27, 27), 1);
+      test('throws an ArgumentError when dividing by zero', () {
+        expect(() => calculator.divide(27, 0), throwsArgumentError);
+      });
     });
 
-    test('the calculator throws an ArgumentError when dividing by zero', () {
-      expect(() => calculator.divide(27, 0), throwsArgumentError);
+    group('powerOfTwo', () {
+      test('returns 81 when the input is 9', () async {
+        expect(await calculator.powerOfTwo(9), 81);
+      });
     });
   });
 }