public function testGetAccessTokenUnitMock()
{
$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('refresh_token' => 'refresh_token_value')));
$response = $auth->getRefreshToken($config, 'auth_value');
$this->assertNotNull($response);
$this->assertEquals('refresh_token_value', $response);
}