What is the test for res judicata?

In Grandview v. Dotting Ritchie J. for the majority of five dealt with a case in which a town was sued for damages for causing a flood. In the first action the town was exonerated. Doering then brought another action alleging the town caused the flood in a different way than was alleged in the first action. Ritchie J. held the second action was barred by res judicata because, while the issue was not dealt with in the first action, it ought to have been. Ritchie J. states at p. 394: “The doctrine of res judicata is founded on public policy so that there may be an end of litigation, and also to prevent the hardship to the individual of being twice vexed for the same cause. The rule which I deduce from the authorities is that a judgment between the same parties is final and conclusive, not only as to the matters dealt with, but also as to questions which the parties had an opportunity of raising. It is clear that the plaintiff must go forward in the first suit with his evidence; he will not be permitted in the event of failure to proceed with a second suit on the ground that he has additional evidence. In order to be at liberty to proceed with a second suit he must be prepared to say: I will show you this is a fact which entirely changes the aspect of the case, and I will show you further that it was not, and could not by reasonable diligence have been ascertained by me before.”