[{"test_results":{"test1":1,"test2":0,"test3":1},"identifier":123},{"test_results":{"test1":0,"test2":1,"test3":0},"identifier":456}]

db.collection.find({},{"_id":0,"ID":{"$cond":{"if":{"$lt":["$test_results.test2",1]},"then":"$identifier","else":null}}})