No they don't.

Can you deny drug test?

You have the right to refuse a drug test, and the employer has the right to refuse you a job on that basis. State laws may impose some procedural rules on how an employer tests. For example, the employer may have to use a certified laboratory or give you an opportunity to explain a positive result.

Do they have to tell you about a drug test?

The constitutional right to privacy almost universally prohibits random drug testing in California. For most jobs, an employer must give notice to all current and prospective employees before a drug test.