GuzzleHttp\Tests\ClientTest::testDoesNotOverwriteHeaderWithDefault PHP Метод

    public function testDoesNotOverwriteHeaderWithDefault()
    {
        $mock = new MockHandler([new Response()]);
        $c = new Client(['headers' => ['User-agent' => 'foo'], 'handler' => $mock]);
        $c->get('http://example.com', ['headers' => ['User-Agent' => 'bar']]);
        $this->assertEquals('bar', $mock->getLastRequest()->getHeaderLine('User-Agent'));
    }