Doctrine\MongoDB\Tests\Aggregation\Stage\ProjectTest::provideAccumulators PHP Method

    public function provideAccumulators()
    {
        $operators = ['avg', 'max', 'min', 'stdDevPop', 'stdDevSamp', 'sum'];
        return array_combine($operators, array_map(function ($operator) {
            return [$operator];
        }, $operators));
    }