Webiny\Component\Http\Request\Headers::get PHP Method

    public function get($key, $value = null)
    {
        return $this->headerBag->key($key, $value, true);
    }

 public function testGet()
 {
     $_SERVER['HTTP_HOST'] = "localhost";
     $headers = new Headers();
     $this->assertSame("localhost", $headers->get("Host"));
     $this->assertNull($headers->get("doesnt_exist"));
     $this->assertSame("utf8", $headers->get("Encoding", "utf8"));
 }