What is the test for determining whether a driver is liable for running over a donkey that has been left out on a public highway?

The case of Davies v. Mann (1842), 10 M. & W. 546, 152 E.R. 588, cited in Salmond's Law of Torts, 6th ed., pp. 38 and 39, is a case in point. "The facts of the case were that the plaintiff negligently left his donkey with its legs tied, in the highway, and the defendant subsequently came past in his wagon and negligently ran over the donkey. It was held that the defendant was liable—notwithstanding the fact that the accident would not have happened but for the contributory negligence of plaintiff—on the ground that the defendant had a sufficient opportunity of avoiding, by the use of reasonable care, the danger so created by the plaintiff's negligence. Although the ass may have been wrongfully there, still the defendant was bound to go along the road at such a pace as would be likely to prevent mischief. Were this not so, a man might justify the driving over goods left on a public highway, or even over a man lying asleep there, or the purposely running against a carriage going on the wrong side of the road."