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Read the description of the union method:


The key words there are this and the other

A perfect example of the use of test cases - failure implies the logic is incorrect somewhere (which is indeed the case). Inspect the methods in the statistician class used prior to that assertion....

Given the number of failures, its probably best to start one at a time. Your union has several assertions - which one fails?

You do not mention which tests fail. This is key to understanding the failures