public function testCustomUserAgent()
{
$guzzle = $this->getGuzzle();
$client = new Client();
$client->setClient($guzzle);
$client->setHeader('User-Agent', 'foo');
$client->request('GET', 'http://www.example.com/');
$this->assertEquals('foo', end($this->history)['request']->getHeaderLine('User-Agent'));
}