diff --git a/app/Billing/FakePaymentGateway.php b/app/Billing/FakePaymentGateway.php
index 668ef62..26182a6 100644
--- a/app/Billing/FakePaymentGateway.php
+++ b/app/Billing/FakePaymentGateway.php
@@ -31,6 +31,13 @@ class FakePaymentGateway implements PaymentGateway
         $this->charges[] = $amount;
     }
 
+    public function newChargesDuring($callback)
+    {
+        $chargesFrom = $this->charges->count();
+        $callback($this);
+        return $this->charges->slice($chargesFrom)->values();
+    }
+
     public function totalCharges()
     {
         return $this->charges->sum();
diff --git a/app/Billing/PaymentGateway.php b/app/Billing/PaymentGateway.php
index b1f5bf8..0ca0840 100644
--- a/app/Billing/PaymentGateway.php
+++ b/app/Billing/PaymentGateway.php
@@ -7,4 +7,5 @@ interface PaymentGateway
     public function charge($amount, $token);
 
     public function getValidTestToken();
+    public function newChargesDuring($callback);
 }
diff --git a/tests/unit/Billing/FakePaymentGatewayTest.php b/tests/unit/Billing/FakePaymentGatewayTest.php
index 42c8c17..c2f4367 100644
--- a/tests/unit/Billing/FakePaymentGatewayTest.php
+++ b/tests/unit/Billing/FakePaymentGatewayTest.php
@@ -13,14 +13,33 @@ class FakePaymentGatewayTest extends TestCase
         return new FakePaymentGateway;
     }
 
+    /** @test */
+    function can_fetch_charges_created_during_a_callback()
+    {
+        $paymentGateway = $this->getPaymentGateway();
+        $paymentGateway->charge(2000, $paymentGateway->getValidTestToken());
+        $paymentGateway->charge(3000, $paymentGateway->getValidTestToken());
+
+        $newCharges = $paymentGateway->newChargesDuring(function ($paymentGateway) {
+            $paymentGateway->charge(4000, $paymentGateway->getValidTestToken());
+            $paymentGateway->charge(5000, $paymentGateway->getValidTestToken());
+        });
+
+        $this->assertCount(2, $newCharges);
+        $this->assertEquals([4000, 5000], $newCharges->all());
+    }
+
     /** @test */
     function charges_with_a_valid_payment_token_are_successful()
     {
         $paymentGateway = $this->getPaymentGateway();
 
-        $paymentGateway->charge(2500, $paymentGateway->getValidTestToken());
+        $newCharges = $paymentGateway->newChargesDuring(function ($paymentGateway) {
+            $paymentGateway->charge(2500, $paymentGateway->getValidTestToken());
+        });
 
-        $this->assertEquals(2500, $paymentGateway->totalCharges());
+        $this->assertCount(1, $newCharges);
+        $this->assertEquals(2500, $newCharges->sum());
     }
 
     /** @test */