Test getting RDF namesapces.
function testGetRdfNamespaces() {
// Get all RDF namespaces.
$ns = rdf_get_namespaces();
$this
->assertEqual($ns['rdfs'], 'http://www.w3.org/2000/01/rdf-schema#', 'A prefix declared once is included.');
$this
->assertEqual($ns['foaf'], 'http://xmlns.com/foaf/0.1/', 'The same prefix declared in several implementations of hook_rdf_namespaces() is valid as long as all the namespaces are the same.');
$this
->assertEqual($ns['foaf1'], 'http://xmlns.com/foaf/0.1/', 'Two prefixes can be assigned the same namespace.');
$this
->assertTrue(!isset($ns['dc']), 'A prefix with conflicting namespaces is discarded.');
}