Doctrine\MongoDB\Tests\Aggregation\Stage\GroupTest::testGroupStage PHP Метод

    public function testGroupStage()
    {
        $groupStage = new Group($this->getTestAggregationBuilder());
        $groupStage->field('_id')->expression('$field')->field('count')->sum(1);
        $this->assertSame(['$group' => ['_id' => '$field', 'count' => ['$sum' => 1]]], $groupStage->getExpression());
    }