使用composer安装依赖，为什么安装了许多没有require的依赖？

{
    "name": "abc",
    "description": "abc",
    "keywords": ["abc"],
    "homepage": "http://www.yiiframework.com/",
    "type": "project",
    "license": "abc",
    "support": {
        "issues": "https://github.com/yiisoft/yii2/issues?state=open",
        "source": "https://github.com/yiisoft/yii2"
    },
    "minimum-stability": "dev",
    "require": {
        "php": ">=5.4.0",
        "yiisoft/yii2": "~2.0.6",
        "yiisoft/yii2-redis": "~2.0.0"
    },
    "require-dev": {
        "yiisoft/yii2-debug": "~2.0.0",
        "yiisoft/yii2-gii": "~2.0.0",
        "yiisoft/yii2-faker": "~2.0.0",
        "codeception/base": "^2.2.3",
        "codeception/verify": "~0.3.1"
    },
    "config": {
        "process-timeout": 1800
    },
    "extra": {
        "asset-installer-paths": {
        }
    },
    "scripts": {
    }
}
composer.json如上图，里面并没有phpunit，symfony等依赖，然而composer install 安装完成后，vendor目录里面多了很多没有require或require-dev里面的依赖，如下图请问下这是什么情况，composer菜鸟求教