Thank you for the information and your question. First you need to ask him what forum you will be testifying in since there are a few different possibilities so I can't guess which one it is. One possibility is that you will be giving a deposition. That is just where either the prosecutor or the defense counsel wants to see what you would say about that night before you actually testify in court. Another possibility is that it is a probable cause
pretrial hearing or grand jury, where they decide whether to issue felony charges. This could also be an evidentiary hearing based on some motion by the defense or prosecution and finally, it could be the actual trial
. So, as you can see, many possibilities and important that you tell them that you aren't interested in talking to them anymore unless they clearly tell you what your statements are needed for.
In addition, if you want, you can refuse to make any more statements unless and until you are subpoenaed as a witness. Once you are subpoenaed you would have to show up. Finally, since you were with this group at one point in the night, and I have no idea what law enforcement thinks you might or might not know or have done, I strongly encourage you to sit down with a local criminal
defense attorney and discuss this issue before you speak to anyone else at all about this case. If the defense attorney thinks that you might be in jeopardy of being charged with something (which is probably not the case, but I don't have all of the facts) then they will try to get you an immunity deal for your testimony. Otherwise, they can advise you on what you should or shouldn't say from here on out.
Please let me know if you need any clarification. I would be glad to assist you further if I can.