A bit shorter with array_diff
$musthave = array('a','b');
$test1 = array('a','b','c');
$test2 = array('a','c');
$containsAllNeeded = 0 == count(array_diff($musthave, $test1));
// this is TRUE
$containsAllNeeded = 0 == count(array_diff($musthave, $test2));
// this is FALSE