SELECT 
  tests_question.tests_list_id, 
  tests_question.tests_question_name, 
  ARRAY( SELECT tests_answer.test_answer_name FROM tests_answer WHERE (tests_answer.tests_question_id = tests_question.tests_question_id)) AS "array" 
FROM tests_question

$query = ("SELECT * FROM test WHERE tests_list_id = ". $_POST['test_id'] ."");
$result = pg_query($query) or die('Ошибка запроса'); 
$array = pg_fetch_all($result);
$my_enc = json_encode($array, JSON_UNESCAPED_UNICODE);