What is the test for constructive knowledge in the context of liability in a motor vehicle accident case?

The court instructed that if the jury found from the evidence that the defective condition of the platform, if found to be defective, had existed for such length of time that the agents or officers of the company, using reasonable care and diligence, would have known about it, then 'that is the same as if they did actually know about it. ' It is said that the court should have defined the circumstances under which there could be such a thing as constructive knowledge, if such knowledge could exist at all. The principle, however, is a familiar one that actual notice of the defective and dangerous condition of a street upon the part of a city is not necessary to be shown in order to hold it liable, for if the agents of the city who are charged with the supervision and control of the streets could, by exercise of reasonable care and diligence, have known of the defective condition, liability may follow. Dallas v. Moore, 32 Tex.Civ.App. 230, 74 S.W. 95. But as the record is made up the plaintiff in error cannot complain, for there was no request for a further instruction upon the point now made.