If you were served with a subpoena, which is a court order to appear in court on a certain date and at a certain time, you are required to appear in court on the date stated on the subpoena. Failure to do so can result in the judge issuing a bench warrant or body attachment for your arrest. The police will be looking for you and when found will arrest you and eventually bring you to court to explain to the judge why you disobeyed the subpoena. The court can find you in contempt of court and sentence you to jail. If you refuse to testify, the court can also find you in contempt and sentence you to jail Since you are a witness and not a defendant or someone charged with a crime, the 5th Amendment will not apply to you. The 5th Amendment only involves protection against self-incrimination. Unless your testimony will in some way incriminate you in the commission of a crime, you cannot use it to avoid testifying.
Answered on Nov 19th, 2013 at 5:41 PM