nl_tokens: Wrap the asCallback function with a check that ensures the callback is never called twice .
pl_tokens: function asCheckedCallback ( promise , cb , useOwnMethod ) { let called = false ; if ( useOwnMethod ) { promise . asCallback ( <mask> ) ; } else { asCallback ( promise , after ) ; } function after ( ) { expect ( called ) . toBeFalsy ( ) ; called = true ; return cb . apply ( this , arguments ) ; } }