public function testZeroFill()
{
$this->assertEquals('0000', StringUtils::zeroFill(''));
$this->assertEquals('0001', StringUtils::zeroFill('1'));
$this->assertEquals('0010', StringUtils::zeroFill(10));
$this->assertEquals('123123', StringUtils::zeroFill('123123'));
$this->assertEquals('00ab', StringUtils::zeroFill('ab'));
$this->assertEquals('000ab', StringUtils::zeroFill('ab', 5));
$this->assertEquals('000000123456', StringUtils::zeroFill('123456', 12));
}