M.P. Sharma vs Satish Chandra, [1954] SCR 1077

Hon’ble Supreme Court of India observed, “Broadly stated, the guarantee in Article 20(3) is against `testimonial compulsion'. It is suggested that this is confined to the oral evidence of a person standing his trial for an offence when called to the witness-stand…..
Indeed, every positive volitional act which furnished evidence is testimony, and testimonial compulsion connotes coercion which procures the positive volitional evidentiary acts of the person, as opposed to the negative attitude of silence or submission on his part….
The phrase used in Article 20(3) is `to be a witness' and not to `appear as a witness'. It follows that the protection afforded to an accused in so far as it is related to the phrase `to be a witness' is not merely in respect of testimonial compulsion in the court room but may well extend to compelled testimony previously obtained from him.”