How do countries know if their economic system is working?

Answer 1

Rate of inflation, employment, imports vs. exports, and how well the rest of the world recognizes and accepts your currency.
Other factors could include gross national product vs, population, per cent of population living in poverty and the size of the middle class if any, but that gets away from economics and into social issues. Socialism is NOT just another type of economic system. It is governmental control over a nations population and life style.
Free enterprise is the only TRUE economic system I can think of. All others have a touch of tyranny involved in them.

Answer 2

if your exports are more than your imports

Answer 3

people are making money.