public function testBasic()
{
$bag = new HeaderBag(['CONTENT_TYPE' => 'application/json', 'Accept' => 'application/json']);
$this->assertEquals(['application/json'], $bag->get('Content-Type'));
$this->assertEquals('application/json', $bag->first('Content-Type'));
$bag->with('Content-Type', 'foo');
$this->assertEquals(['application/json', 'foo'], $bag->get('Content-Type'));
}