function testAddHeaders()
{
$message = new MessageMock();
$message->addHeaders(['a' => 'b']);
$message->addHeaders(['c' => 'd']);
$this->assertEquals('b', $message->getHeader('a'));
}
function testMultipleHeaders()
{
$message = new MessageMock();
$message->setHeader('a', '1');
$message->addHeader('A', '2');
$this->assertEquals("1,2", $message->getHeader('A'));
$this->assertEquals("1,2", $message->getHeader('a'));
$this->assertEquals(['1', '2'], $message->getHeaderAsArray('a'));
$this->assertEquals(['1', '2'], $message->getHeaderAsArray('A'));
$this->assertEquals([], $message->getHeaderAsArray('B'));
}