PHPUnit testing a protected static method that uses pdo - pdo

Question

I am very new to TDD. I am using phpunit 7.4x-dev. I have the following abstract class that I am trying to develop unit tests for.
use PDO;
abstract class Model {
protected static function getDB() {
static $db = null;
if ($db === null) {
$db = new PDO(ConfigDatabase::DSN, ConfigDatabase::USER, ConfigDatabase::PASSWORD);
$db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}
return $db;
}
}
I have created the following test to get around the need to deal with the static protected method. And it works if I provide "ConfigureDatabase" class.
use PHPUnit\Framework\TestCase;
class ModelTest extends TestCase {
function newMockClass(){
$stub = new class() extends Model{
function getStaticMethod($methodName){
return self::$methodName();
}
};
return $stub;
}
public function testDatabaseExists() {
$stub = $this->newMockClass();
$db = $stub->getStaticMethod('getDB');
$this->assertInstanceOf(PDO::class,$db);
}
}
Since I do not want my tests to rely on any actual database, How would I fake the calls to PDO.

Answer 1

Following Dormilich suggestion I developed a database interface, just in case I decide later I do not want to use PDO.
interface CRUDImp {
function __construct($datbaseBridgeLikePDO);
...
}
Next I wrote my tests for the constructor. I used setup to make sure I was starting with a fresh mock of \PDO.
class PDOWrapperTest extends TestCase {
private $pdoMock;
private $db;
function setup() {
$this->pdoMock = $this->createMock('\PDO');
$this->db = new PDOWrapper($this->pdoMock);
}
public function testWrapperExists() {
$this->pdoMock->method('getAttribute')->willReturn(\PDO::ERRMODE_EXCEPTION);
$db = new PDOWrapper($this->pdoMock);
$x = $db instanceof CRUDImp;
$this->assertTrue($x);
}
/**
* #expectedException \Exception
*/
public function testNonPDOPassedToConstructor() {
$mock = $this->createMock('\Exception');
$x = new PDOWrapper($mock);
}
...
}
Since PHP is loosely typed I check to make sure that the class passed to the constructor was an instance of \PDO. I implemented the concrete class as follows
class PDOWrapper implements CRUDImp {
private $pdo;
private $dataOutputType = \PDO::FETCH_ASSOC;
public function __construct($pdo) {
if (!($pdo instanceof \PDO)) {
throw new \Exception("PDOWrapper must be passed instance of \PDO");
}
$attr_Errmode = $pdo->getAttribute(\PDO::ATTR_ERRMODE);
if ($attr_Errmode !== \PDO::ERRMODE_EXCEPTION) {
$pdo->setAttribute(\PDO::ATTR_ERRMODE, \PDO::ERRMODE_EXCEPTION);
}
$this->pdo = $pdo;
}
...
}
Now that I have an independent database wrapper the original Model tests are at the moment trivial and no longer needed. The abstract class Model was modified as follows:
abstract class Model {
protected $database=null;
function __construct(CRUDWrapper $database) {
$this->database = $database;
}
...
}
So for those not familiar with dependency injection I found the following links helpful:
http://php-di.org/doc/understanding-di.html
https://codeinphp.github.io/post/dependency-injection-in-php/
https://designpatternsphp.readthedocs.io/en/latest/Structural/DependencyInjection/README.html
Hope this shortens someone's work.