public function testLookupStage() { $lookupStage = new Lookup($this->getTestAggregationBuilder(), 'collection'); $lookupStage->localField('local.field')->foreignField('foreign.field')->alias('lookedUp'); $this->assertSame(['$lookup' => ['from' => 'collection', 'localField' => 'local.field', 'foreignField' => 'foreign.field', 'as' => 'lookedUp']], $lookupStage->getExpression()); }