Griselda marries Gualtieri, the Marquis of Saluzzo tests her by declaring that their two children--a son and a daughter--must both be put to death.
Griselda marries Gualtieri tests her by. Their two children--a son and a daughter--must both be put to death. This was what Griselda marries Gualtieri was declaring. Griselda marries Gualtieri is the Marquis of Saluzzo.