What is the test for compelling a witness in a criminal case?

The order entered here did not compel "communications" or "testimony" on the issue of guilt of the defendant. It may be likened to compelling blood tests, handwriting exemplars, "fingerprinting, photographing or measurements, to write or speak for identification, to appear in court, to stand, to assume a stance, to walk, or to make a particular gesture."^2a Schmerber v. California, 384 U.S. 757, 86 S.Ct. 1826, 16 L.Ed.2d 908 (1966). See also Gilbert v. California, 388 U.S. 263, 87 S.Ct. 1951, 18 L.Ed.2d 1178 (1967).