Posting an XML request using HTTP API

I figured it out. The WordPress HTTP API was doing it’s job; my problem was with the API I was working with. I just modified my code like:

$url="https://www.testurl.com";
$xml = <<<TESTED XML HERE>>>;
$response = wp_remote_post( 
    $url, 
    array(
        'method' => 'POST',
        'timeout' => 45,
        'redirection' => 5,
        'httpversion' => '1.0',
        'headers' => array(
            'Content-Type' => 'text/xml'
        ),
        'body' => array('postdata' => $xml, 'postfield' => 'value'),
        'sslverify' => false
    )
);

Again…this was just a misunderstand of the API I was working with, not the HTTP API provided my WordPress.

Edit:
POST data should be supplied as an array, according to http://codex.wordpress.org/Function_API/wp_remote_post
The array will be transformed into a string like this:
key1=val1&key2=val2&…