Final answer:
The best test of an economic theory is its ability to predict real-world events. Theories are constantly evaluated against actual data to gauge their effectiveness, with successful prediction being the key indicator of their validity.
Step-by-step explanation:
The best test of an economic theory is d) the ability of the theory to predict real-world events. This is because economics aims to explain and predict human behavior within markets and the economy at large. The core purpose of an economic theory is to provide insight into how individuals, businesses, and governments will act under certain circumstances and to anticipate the outcomes of these actions. While the underlying assumptions (option b) and the implications for public policy (option a) are important, they are not the definitive test of a theory's validity. The complexity and mathematical detail behind the theory (option c) add rigor but do not necessarily make for better predictions.
An economist, for example, may develop a model to forecast stock market trends and compare the predicted results to actual market performance. Similarly, well-known economic theories, such as supply and demand, are constantly tested against real-world data to assess their predictive power.