public function testUpdateAccessTokenNullReturnUnitMock()
{
$config = array('mode' => 'sandbox');
/** @var OAuthTokenCredential $auth */
$auth = $this->getMockBuilder('\\PayPal\\Auth\\OAuthTokenCredential')->setConstructorArgs(array('clientId', 'clientSecret'))->setMethods(array('getToken'))->getMock();
$auth->expects($this->any())->method('getToken')->will($this->returnValue(array()));
$response = $auth->updateAccessToken($config);
$this->assertNotNull($response);
$this->assertEquals('accessToken', $response);
}