我已经安装了 Laravel 5.6 的干净版本。然后我成功安装了 Behat，输出如下。
composer require behat/behat behat/mink behat/mink-extension laracasts/behat-laravel-extension --dev
Using version ^3.4 for behat/behat
Using version ^1.7 for behat/mink
Using version ^2.3 for behat/mink-extension
Using version ^1.1 for laracasts/behat-laravel-extension
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Package operations: 15 installs, 0 updates, 0 removals
- Installing symfony/dom-crawler (v4.1.2): Downloading (100%)
- Installing behat/mink (dev-master d5ee350): Cloning d5ee350c40
- Installing symfony/browser-kit (v4.1.2): Downloading (100%)
- Installing behat/mink-browserkit-driver (1.3.3): Downloading (100%)
- …