public function testExpressionSelectExpression()
 {
     $this->assertEquals('(SUM(field1) + SUM(field2)) AS sum_field', QueryAssembler::stringify(ExpressionSelectExpression::createWithAlias(AdditionExpression::create(SumSelectExpression::create('field1'), SumSelectExpression::create('field2')), 'sum_field')));
     $this->assertEquals('SELECT (SUM(field1) + SUM(field2)) AS sum_field FROM tbl HAVING sum_field >= 5', QueryAssembler::stringify(QueryBuilder::select(ExpressionSelectExpression::createWithAlias(AdditionExpression::create(SumSelectExpression::create('field1'), SumSelectExpression::create('field2')), 'sum_field'))->from('tbl')->having(GreaterThanOrEqualPredicate::create('sum_field', 5))));
 }