Can a cop leave his test tube in my car?

Call and hire an attorney.

Come and hire me.

To answer your question you really need to hire an attorney as soon as possible. At this stage the state attorneys office will be reviewing the case to decide whether or not to proceed with prosecution. An attorney would know how to make sure the prosecutors are aware of any defenses you might have as well as keep you advised on how to proceed. If the marijuana was located and recovered by the police in an automobile there may be issues involving search and seizure or constructive possession which would allow for motions to suppress or dismiss the charge, should it be filed. As far as the test tube is concerned, it would be unusual if the police officer left it in your car but that test is simply a presumptive field test which the police use to establish probable cause to arrest you. That test would not be admissible in court against you and would not be considered evidence in your case. Are you sure that the police officer did not recover additional amounts of marijuana which he or she took with him? If so, that marijuana would be kept as evidence and sent to the crime lab for professional lab tests and then used against you as evidence. Again, the issues in a case like this or complex enough that you should not attempt to represent yourself, if you cannot afford to hire an attorney, then be grateful for your public defender and give him or her your full cooperation. Good luck.