Run method for a test suite (currently only supporting Mocha)
@param {Function|String} engineName If a function, Skeleton will process via it. Otherwise, Skeleton will retrieve the engine from its modules.
@returns {Mixed} Returns result of engine
function (engineName) {
    var engine = engineName;

    // If the engine is not a function, retrieve it from the modules
    if (typeof engine !== 'function') {
      engine = Skeleton.modules[engineName];
    }

    // If the engine is not a function, throw an error
    if (typeof engine !== 'function') {
      throw new Error('Test engine was not found: ' + engineName);
    }

    // Run and return the engine in the context of this with batches as the first parameter
    return engine.call(this, this.batches);
  }