function testDeleteAll()
{
//Arrange
$book_id = 1;
$due_date = '0000-00-00';
$id = 1;
$test_copy = new Copy($book_id, $due_date, $id);
$test_copy->save();
$book_id2 = 2;
$due_date2 = '0000-00-00';
$id2 = 2;
$test_copy2 = new Copy($book_id2, $due_date2, $id2);
$test_copy2->save();
//Act
Copy::deleteALl();
//Assert
$result = Copy::getAll();
$this->assertEquals([], $result);
}
