public function testHeaderRemovalIsCaseInsensitive()
{
$message = $this->message->withHeader('X-Foo', 'Foo')->withAddedHeader('x-foo', 'Bar')->withAddedHeader('X-FOO', 'Baz');
$this->assertNotSame($this->message, $message);
$this->assertTrue($message->hasHeader('x-foo'));
$message2 = $message->withoutHeader('x-foo');
$this->assertNotSame($this->message, $message2);
$this->assertNotSame($message, $message2);
$this->assertFalse($message2->hasHeader('X-Foo'));
$headers = $message2->getHeaders();
$this->assertEquals(0, count($headers));
}