public function multipleHeadersOfTheSameNameMayBeDefined()
{
$message = $this->getAbstractMessageMock();
$message->setHeader('MyHeader', 'MyValue', false);
$message->setHeader('MyHeader', 'OtherValue', false);
$expectedHeaders = ['MyHeader' => ['MyValue', 'OtherValue']];
$this->assertEquals($expectedHeaders, $message->getHeaders()->getAll());
}