Failing assertion provides bad test result

[Almad]

  1) Drafter Class parses and expands a blueprint:
     Uncaught Error: Callback was already called.
    at /Users/almad/Documents/projects/drafter.js/node_modules/async/lib/async.js:30:31
    at /Users/almad/Documents/projects/drafter.js/src/drafter.coffee:170:7
    at /Users/almad/Documents/projects/drafter.js/src/drafter.coffee:87:5
    at /Users/almad/Documents/projects/drafter.js/node_modules/boutique/lib/index.js:53:14
    at json (/Users/almad/Documents/projects/drafter.js/node_modules/boutique/lib/serializers.js:10:12)
    at /Users/almad/Documents/projects/drafter.js/node_modules/boutique/lib/index.js:50:16
    at fn (/Users/almad/Documents/projects/drafter.js/node_modules/async/lib/async.js:641:34)
    at Object._onImmediate (/Users/almad/Documents/projects/drafter.js/node_modules/async/lib/async.js:557:34)
    at processImmediate [as _immediateCallback] (timers.js:354:15)

[Almad]

Actually a code issue, will reopen with tests.