图片文件验证问题

表单上传一些文本和图片，下面是控制器代码，如果有图片上传，可以正常跑通，但测试如果不上传图片，会重定向到首页，说好的报错不知道报到哪里去了。

    public function store(Requests\StoreArticlePostRequest $request)
    {
        $article = new Article($request->except('image'));
        $article->user_id = \Auth::id();

        if ($request->hasFile('image')) {
            $file = $request->file('image');
            $allowed_extensions = ["png", "jpg"];
            if ($file->getClientOriginalExtension() && !in_array($file->getClientOriginalExtension(), $allowed_extensions)) {
                return ['error' => '图片格式只能为png、jpg'];
            }

            $extension = $file -> getClientOriginalExtension();
            $fileName = \Auth::user()->id . '_' . time() . '.' . $extension;
            $destinationPath = 'uploads/' . $article->user_id . '/';
            $file->move($destinationPath, $fileName);
            $article->picture = $fileName;
            $article->save();
        } else {
            echo "必须上传图片";
        }
        return redirect()->action('PostsController@show', ['id' => $article->id]);
    }