diff --git a/app/Billing/FakePaymentGateway.php b/app/Billing/FakePaymentGateway.php
index 26182a6..c53b432 100644
--- a/app/Billing/FakePaymentGateway.php
+++ b/app/Billing/FakePaymentGateway.php
@@ -35,7 +35,7 @@ class FakePaymentGateway implements PaymentGateway
     {
         $chargesFrom = $this->charges->count();
         $callback($this);
-        return $this->charges->slice($chargesFrom)->values();
+        return $this->charges->slice($chargesFrom)->reverse()->values();
     }
 
     public function totalCharges()
diff --git a/composer.json b/composer.json
index 3bec5de..b37808f 100644
--- a/composer.json
+++ b/composer.json
@@ -28,7 +28,7 @@
     },
     "autoload-dev": {
         "classmap": [
-            "tests/TestCase.php"
+            "tests"
         ]
     },
     "scripts": {
diff --git a/tests/unit/Billing/FakePaymentGatewayTest.php b/tests/unit/Billing/FakePaymentGatewayTest.php
index c2f4367..f623a82 100644
--- a/tests/unit/Billing/FakePaymentGatewayTest.php
+++ b/tests/unit/Billing/FakePaymentGatewayTest.php
@@ -8,40 +8,13 @@ use Illuminate\Foundation\Testing\DatabaseTransactions;
 
 class FakePaymentGatewayTest extends TestCase
 {
+    use PaymentGatewayContractTests;
+
     protected function getPaymentGateway()
     {
         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();
-
-        $newCharges = $paymentGateway->newChargesDuring(function ($paymentGateway) {
-            $paymentGateway->charge(2500, $paymentGateway->getValidTestToken());
-        });
-
-        $this->assertCount(1, $newCharges);
-        $this->assertEquals(2500, $newCharges->sum());
-    }
-
     /** @test */
     function charges_with_an_invalid_payment_token_fail()
     {
diff --git a/tests/unit/Billing/PaymentGatewayContractTests.php b/tests/unit/Billing/PaymentGatewayContractTests.php
new file mode 100644
index 0000000..1c3b4cb
--- /dev/null
+++ b/tests/unit/Billing/PaymentGatewayContractTests.php
@@ -0,0 +1,35 @@
+<?php
+
+trait PaymentGatewayContractTests
+{
+    abstract protected function getPaymentGateway();
+
+    /** @test */
+    function charges_with_a_valid_payment_token_are_successful()
+    {
+        $paymentGateway = $this->getPaymentGateway();
+
+        $newCharges = $paymentGateway->newChargesDuring(function ($paymentGateway) {
+            $paymentGateway->charge(2500, $paymentGateway->getValidTestToken());
+        });
+
+        $this->assertCount(1, $newCharges);
+        $this->assertEquals(2500, $newCharges->sum());
+    }
+
+    /** @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([5000, 4000], $newCharges->all());
+    }
+}
diff --git a/tests/unit/Billing/StripePaymentGatewayTest.php b/tests/unit/Billing/StripePaymentGatewayTest.php
index e17f353..829a441 100644
--- a/tests/unit/Billing/StripePaymentGatewayTest.php
+++ b/tests/unit/Billing/StripePaymentGatewayTest.php
@@ -8,6 +8,8 @@ use App\Billing\PaymentFailedException;
  */
 class StripePaymentGatewayTest extends TestCase
 {
+    use PaymentGatewayContractTests;
+
     protected function setUp()
     {
         parent::setUp();
@@ -19,19 +21,6 @@ class StripePaymentGatewayTest extends TestCase
         return new StripePaymentGateway(config('services.stripe.secret'));
     }
 
-    /** @test */
-    function charges_with_a_valid_payment_token_are_successful()
-    {
-        $paymentGateway = $this->getPaymentGateway();
-
-        $newCharges = $paymentGateway->newChargesDuring(function ($paymentGateway) {
-            $paymentGateway->charge(2500, $paymentGateway->getValidTestToken());
-        });
-
-        $this->assertCount(1, $newCharges);
-        $this->assertEquals(2500, $newCharges->sum());
-    }
-
     /** @test */
     function charges_with_an_invalid_payment_token_fail()
     {