public function testAssemble()
 {
     $selector = new FormatSelectExpression();
     $selector->setField('fieldname');
     $this->assertEquals('FORMAT(fieldname)', QueryAssembler::stringify($selector));
     $selector->setAlias('rnd');
     $this->assertEquals('FORMAT(fieldname) AS rnd', QueryAssembler::stringify($selector));
     $selector->setPrecision(2);
     $this->assertEquals('FORMAT(fieldname,2) AS rnd', QueryAssembler::stringify($selector));
 }