Use single connection MySQL driver in test env

.travis.yml

@@ -10,6 +10,7 @@ matrix:
         - php: 5.5
 
 before_script:
+    - "ulimit -n 10000"
     - "sudo apt-get install -y wkhtmltopdf"
     - "export DISPLAY=:99.0"
     - "sh -e /etc/init.d/xvfb start"

app/config/config_test.yml

@@ -17,6 +17,7 @@ swiftmailer:
 doctrine:
     dbal:
         dbname:   %sylius.database.name%_test
+        driver_class: Sylius\Bundle\CoreBundle\Tests\MySqlDriver
 
 sylius_money:
     currency: EUR

src/Sylius/Bundle/CoreBundle/Tests/MySqlDriver.php

@@ -0,0 +1,19 @@
+<?php
+
+namespace Sylius\Bundle\CoreBundle\Tests;
+
+use Doctrine\DBAL\Driver\PDOMySql\Driver;
+
+class MySqlDriver extends Driver
+{
+    private static $connection;
+
+    public function connect(array $params, $username = null, $password = null, array $driverOptions = array())
+    {
+        if (null === self::$connection) {
+            self::$connection = parent::connect($params, $username, $password, $driverOptions);
+        }
+
+        return self::$connection;
+    }
+}