Use instance in query if there are more than one instances and add tests

src/Cart.php

@@ -831,7 +831,11 @@ class Cart
      */
     private function storedCartWithIdentifierExists($identifier)
     {
-        return $this->getConnection()->table($this->getTableName())->where('identifier', $identifier)->where('instance', $this->currentInstance())->exists();
+        $data = ['identifier' => $identifier];
+        if ($this->countInstances() > 1) {
+            $data['instance'] = $this->currentInstance();
+        }
+        return $this->getConnection()->table($this->getTableName())->where($data)->exists();
     }
 
     /**

tests/CartTest.php

@@ -1453,4 +1453,36 @@ class CartTest extends TestCase
         $this->app['config']->set('cart.format.decimal_point', $decimalPoint);
         $this->app['config']->set('cart.format.thousand_separator', $thousandSeperator);
     }
+
+    /** @test */
+    public function it_can_store__mutiple_instances_of_the_cart_in_a_database()
+    {
+        $this->artisan('migrate', [
+            '--database' => 'testing',
+        ]);
+
+        Event::fake();
+
+        $cart = $this->getCart();
+
+        $cart->add(new BuyableProduct());
+
+        $cart->store($identifier = 123);
+
+        $serialized = serialize($cart->content());
+
+        $newInstance = $this->getCart();
+        $newInstance->instance($instanceName = 'someinstance');
+        $newInstance->add(new BuyableProduct());
+        $newInstance->store($newIdentifier = 456);
+        $newInstanceSerialized = serialize($newInstance->content());
+
+        $this->assertDatabaseCount('shoppingcart', 2);
+
+        $this->assertDatabaseHas('shoppingcart', ['identifier' => $identifier, 'instance' => 'default', 'content' => $serialized]);
+
+        $this->assertDatabaseHas('shoppingcart', ['identifier' => $newIdentifier, 'instance' => $instanceName, 'content' => $newInstanceSerialized]);
+
+        Event::assertDispatched('cart.stored');
+    }
 }