Laravel 5 在laravel 5.8 phpunit测试中，控制器在雄辩的查询中返回null

我正在尝试为模型

ProjectRating

创建一个模拟，其中我希望根据模型的查询返回一个特定值。使用

select

和

first

时，我接收到设置的结果值，但当查询中有

where

时，我将得到null

我在控制器中的查询如下所示

$projectRating = ProjectRating::select('rating')
                ->where('project_id', $projectId)
                ->where('country_id', $countryId)
                ->where('language_id', $languageId)
                ->first() ;

$fakeProjectRating = \Mockery::mock(ProjectRating::class);

$fakeProjectRating->shouldReceive('select->where->where->where->first')->andReturn(['rating'=>'c']);

app()->instance(ProjectRating::class, $fakeProjectRating);

我的测试代码如下所示

$projectRating = ProjectRating::select('rating')
                ->where('project_id', $projectId)
                ->where('country_id', $countryId)
                ->where('language_id', $languageId)
                ->first() ;

$fakeProjectRating = \Mockery::mock(ProjectRating::class);

$fakeProjectRating->shouldReceive('select->where->where->where->first')->andReturn(['rating'=>'c']);

app()->instance(ProjectRating::class, $fakeProjectRating);

提前谢谢