Doctrine\MongoDB\Tests\Aggregation\Stage\GroupTest::testGroupFromBuilder PHP Method

    public function testGroupFromBuilder()
    {
        $builder = $this->getTestAggregationBuilder();
        $builder->group()->field('_id')->expression('$field')->field('count')->sum(1);
        $this->assertSame([['$group' => ['_id' => '$field', 'count' => ['$sum' => 1]]]], $builder->getPipeline());
    }