public function testSerializesMultipleHeadersCorrectly()
{
$response = (new Response())->withStatus(204)->withAddedHeader('X-Foo-Bar', 'Baz')->withAddedHeader('X-Foo-Bar', 'Bat');
$message = Serializer::toString($response);
$this->assertContains("X-Foo-Bar: Baz", $message);
$this->assertContains("X-Foo-Bar: Bat", $message);
}