add functional driver test case for ibm_db2 driver

tests/Doctrine/Tests/DBAL/Functional/Driver/IBMDB2/DB2DriverTest.php

+<?php
+
+namespace Doctrine\Tests\DBAL\Functional\Driver\Mysqli;
+
+use Doctrine\DBAL\Driver\IBMDB2\DB2Driver;
+use Doctrine\Tests\DBAL\Functional\Driver\AbstractDriverTest;
+
+class DB2DriverTest extends AbstractDriverTest
+{
+    protected function setUp()
+    {
+        if (! extension_loaded('ibm_db2')) {
+            $this->markTestSkipped('ibm_db2 is not installed.');
+        }
+
+        parent::setUp();
+
+        if (! $this->_conn->getDriver() instanceof DB2Driver) {
+            $this->markTestSkipped('ibm_db2 only test.');
+        }
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function testConnectsWithoutDatabaseNameParameter()
+    {
+        $this->markTestSkipped('IBM DB2 does not support connecting without database name.');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    public function testReturnsDatabaseNameWithoutDatabaseNameParameter()
+    {
+        $this->markTestSkipped('IBM DB2 does not support connecting without database name.');
+    }
+
+    /**
+     * {@inheritdoc}
+     */
+    protected function createDriver()
+    {
+        return new DB2Driver();
+    }
+}