Doctrine\MongoDB\Aggregation\Stage\Project::getExpression PHP Method

    public function getExpression()
    {
        return ['$project' => $this->expr->getExpression()];
    }

 /**
  * @dataProvider provideAccumulators
  */
 public function testAccumulatorsWithMultipleArguments($operator)
 {
     $projectStage = new Project($this->getTestAggregationBuilder());
     $projectStage->field('something')->{$operator}('$expression1', '$expression2');
     $this->assertSame(array('$project' => array('something' => array('$' . $operator => array('$expression1', '$expression2')))), $projectStage->getExpression());
 }