Before Wp 3.2 any textarea can be changed into a tiny-mce editor by adding the class =’theEditor’
But in recent versions it didn’t work as expected. So after lot of search i found that WP have included a new function to convert any metabox to editor.
the arguments are
$content is the content inside textarea which can retrieved from a post meta or any post content
‘test_content’ is id
$settings for additional options
wp_editor( $content, 'test_content', $settings = array('textarea_name'=>'test_content','textarea_rows'=>10) );