Add tests to the tests.TestProblemSet class that will test a static method named average in the ratings.ProblemSet class

The average method will take an ArrayList of Doubles as a parameter and returns the average of the values in the ArrayList as a double

If the ArrayList is empty, the method should return $0\mathrm{.}0$

Examples:

average$([1\mathrm{.}0,2\mathrm{.}0,3\mathrm{.}0])$ returns $2\mathrm{.}0$

average$([-5\mathrm{.}0,5\mathrm{.}0])$ returns $0\mathrm{.}0$

average$([6\mathrm{.}5,6\mathrm{.}5,8\mathrm{.}5,8\mathrm{.}5])$ returns $7\mathrm{.}5$

average$([])$ returns $0\mathrm{.}0$