function testAddHeaders()
{
$message = new MessageMock();
$message->addHeaders(['a' => 'b']);
$message->addHeaders(['c' => 'd']);
$this->assertEquals('b', $message->getHeader('a'));
}
function testAddHeaders()
{
$message = new MessageMock();
$headers = ['X-Foo' => ['1'], 'X-Bar' => ['2']];
$message->addHeaders($headers);
$this->assertEquals($headers, $message->getHeaders());
$message->addHeaders(['X-Foo' => ['3', '4'], 'X-Bar' => '5']);
$expected = ['X-Foo' => ['1', '3', '4'], 'X-Bar' => ['2', '5']];
$this->assertEquals($expected, $message->getHeaders());
}