Fix to off-by-one for TopK and related test cases

[jonahharris]

After playing with the TopK example, I realized the output was not as expected. After looking into this, it's because the iteration used to pull the items out of the heap was using an improper lower bound index of greater than zero. The test cases passed because they only evaluated in comparison to the expected values by order of those returned by TopK instead of using the expected as the baseline, which meant the missing value was not found in the test cases. Accordingly, I updated the test cases to include the actual vs. expected length of the .values() and .iterator(). Likewise, iterator was being used in the first values test case, which was also incorrect.