The realism of the assumptions is the best test of an economic theory. When deciding how to allocate time, the concept of opportunity cost is meaningless. When deciding whether to purchase a second order of Cheese Fries at Joe's, the economic way of thinking indicates that the consumer should compare the benefits expected from two plates of Cheese Fries with the cost of both. Having airlines notify the FAA of flight cancellations so that air traffic controllers can make more efficient use of scarce airspace illustrates the economic principle that Air is a free good Secondary effects are usually unimportant. The true test of a theory is its ability to predict.
Information is an economic good.
The value of a good depends on many factors, including who uses it and under what circumstances. Thoughtful people oppose farm subsidies. Rapid growth of the money supply will cause inflation. The sales tax on food should be repealed. The increase in the cost of medical care must be slowed.