There is a distinction between screening and diagnostic testing.
Certainly, if TB is a possible diagnosis that needs to be evaluated, then TB testing is covered. However, if one is simply screening for TB (out of curiosity, or for employment reasons, for example, and in the absence of signs, symptoms, or increased risk of disease, i.e. exposure to TB) then it would not likely be covered.
If you review the CMS Guide of Medicare Preventive Services, you won't find a provision for TB screening.