Tests having queries.
function testHavingCountQuery() {
$query = db_select('test')
->extend('Drupal\\Core\\Database\\Query\\PagerSelectExtender')
->groupBy('age')
->having('age + 1 > 0');
$query
->addField('test', 'age');
$query
->addExpression('age + 1');
$count = count($query
->execute()
->fetchCol());
$this
->assertEqual($count, 4, 'Counted the correct number of records.');
}