callHelp(options) {
    let environment = options.environment;
    let commandName = options.commandName;
    let commandArgs = options.commandArgs;
    let helpIndex = commandArgs.indexOf('--help');
    let hIndex = commandArgs.indexOf('-h');

    let HelpCommand = lookupCommand(environment.commands, 'help', commandArgs, {
      project: environment.project,
      ui: this.ui,
    });

    let help = new HelpCommand({
      ui: this.ui,
      commands: environment.commands,
      tasks: environment.tasks,
      project: environment.project,
      settings: environment.settings,
      testing: this.testing,
    });

    if (helpIndex > -1) {
      commandArgs.splice(helpIndex, 1);
    }

    if (hIndex > -1) {
      commandArgs.splice(hIndex, 1);
    }

    commandArgs.unshift(commandName);

    return help.validateAndRun(commandArgs);
  }
@private
@method callHelp
@param options
@return {Promise}