Test that we can alter the fields of a query.
function testAlterChangeFields() {
$query = db_select('test');
$name_field = $query
->addField('test', 'name');
$age_field = $query
->addField('test', 'age', 'age');
$query
->orderBy('name');
$query
->addTag('database_test_alter_change_fields');
$record = $query
->execute()
->fetch();
$this
->assertEqual($record->{$name_field}, 'George', 'Correct data retrieved.');
$this
->assertFalse(isset($record->{$age_field}), 'Age field not found, as intended.');
}