Can I refuse a **** test without losing my job?

No. Employers may set terms or conditions on employment. One term or condition may be taking (and presumably passing) a drug or other similar test. (The computer system "asteriked out" the type of test you are asking about, so I am guessing as to what it is.) Employers may, in the absence of a contract, generally fire employees anytime, for any reason, including violating various terms or conditions of employment.

Most employment relationships are what is known as "at will".  This means that basically the employer can hire or fire someone for any reason or no reason whatsoever, as well has increase/decrease salary/hours, promote/demote, and generally impose requirements as they see fit.  In turn, you can work for an employer, or not, your choice. 

The only exceptions to the above would be if there is a stated company policy covering this, or there is a union/employment agreement that governs, or this situation has arisen due to some type of discrimination.