I thought that no body has ever caught hiv through a shared cocaine straw. You said, it is wise to get tested if ever a cocaine straw was shared. Why?
Cocaine by itself is considered a risk factor for acquiring HIV mainly because there is an association of unprotected sex and drug use. People are more likely to engage in risky behaviors when they are intoxicated or "high" on drugs. Hepatitis C has been reported to be transmitted by sharing straws. It is plausible that if blood is on the straw that one could transmit HIV but I would worry about hepatitis B and C more. Best advice is not to share straws and reduce your risks.