If a 911 Caller Gets Subpoena To Court Do They Have The Right NOT To Testify?

Do they have the right NOT to testify all they did was dial 911 they didn't see anything but a gun and shots getting fired and a dead floor on the body but they didn't see the shooter and the detective never came to show a line up of the suspect so how would that play out in court? This is in the state of ohio!