code: function(dependency, message) {
        hook('requiring', dependency, message)
        try { eval(dependency) }
        catch (e) { throw 'JSpec depends on ' + dependency + ' ' + message }
        return this
      }
docs: Require a dependency, with optional message.
  
  @param  {string} dependency
  @param  {string} message (optional)
  @return {JSpec}
  @api public