What is a "Cornucopian government"?

Other versions of this IELTS question found on Google Books appear to indicate that it is likely a name of an imaginary country used to create a hypothetical scenario for the question. (See this comment by Laurel who first made the observation).

To end something suddenly and finally. The Cornucopian government decided to _____ relations with Utopia.

This also answers the question about why "Cornucopian" was capitalized, just as one would write "The American government..."

But the IELTS question as worded in the question is confusing to a native reader who might be aware of "cornucopian" in the context of economics and futurism, which as the OP points out, is a real term that refers to those holding a belief that technology will solve problems of resource management and rapid population growth.

The subject is discussed in depth on Wikipedia, with reputable sources linked.

A cornucopian is a futurist who believes that continued progress and provision of material items for mankind can be met by similarly continued advances in technology. Fundamentally they believe that there is enough matter and energy on the Earth to provide for the population of the world.

A similar technical definition is not found in the OED or other dictionaries that I checked, so I assume that it is a very esoteric term.

In conclusion, I would not recommend trying to explain the term to students learning English beyond perhaps describing how the fictional country name derives from the word "cornucopia," along with any requisite explanation of cornucopias.