Historically, a wife could not be compelled to testify against her husband. This is no longer the case.
A close relative of a person charged with a criminal offence is regarded as competent and compellable to give evidence against that person [s 21 (1) Evidence Act 1929 (SA)]. A close relative can be a spouse, domestic partner, child or parent of the accused [s 21(9)] .
In certain circumstances a close relative who is called as a witness may be excused from giving evidence and can apply for an exemption [s 21(2)].
When considering whether to excuse such a witness, the judge must consider the risk of substantial harm to the relationship between the prospective witness and the accused and whether the witness is likely to suffer serious material, emotional or psychological harm by being compelled to give evidence. These factors have to be weighed against the gravity and the nature of the offence [s 21(3)].
A judge can grant this exemption, even where an application hasn't been made if the prospective witness is a young child (14 years old or under) or is cognitively impaired [s 21(4)].