Sokil\Mongo\Pipeline::project PHP Method

    public function project(array $pipeline)
    {
        $this->addStage('$project', $pipeline);
        return $this;
    }

 /**
  * Check if pipeline added as new or appended to previouse on same operator
  */
 public function testPipeline_ToString()
 {
     $pipeline = new Pipeline($this->collection);
     // insert new match pipeline
     $pipeline->match(array('field1' => 'value1'));
     // insert new project pipeline
     $pipeline->project(array('field2' => 'value2'));
     // insert new match pipeline
     $pipeline->match(array('field3' => 'value3'));
     // append match pipeline to previous
     $pipeline->match(array('field3' => 'value3merged', 'field4' => 'value4'));
     // insert new sort pipeline
     $pipeline->sort(array('field5' => 'value5'));
     // insert new group pipeline
     $pipeline->group(array('_id' => '$groupField', 'field6' => array('$sum' => 1)));
     $validJson = '[{"$match":{"field1":"value1"}},{"$project":{"field2":"value2"}},{"$match":{"field3":"value3merged","field4":"value4"}},{"$sort":{"field5":"value5"}},{"$group":{"_id":"$groupField","field6":{"$sum":1}}}]';
     $this->assertEquals($validJson, $pipeline->__toString());
 }