CS:
I think the labeling in the error message is reversed for the following tests: RandomBig, RandomFull, RandomTestsAlmostEmpty, and RandomTestsManyShare

Example:
RandomTestsAlmostEmpty

Test Failed
Expected: null

But was: < 66, 16, 4, 55, 76, 55, 36, 5, 34, 1, 35, 57, 60, 86, 6, 12, 16, 66, 60, 26, 19, 84, 40, 66, 26, 43, 26, 60, 26, 66, 43, 23, 77, 26, 50, 23, 66, 60, 74, 88, 43, 23, 12, 38, 6, 60, 85, 43, 57, 60, 6, 38, 21, 32, 20, 50, 74, 50, 50, 16, 40, 6, 2, 79, 43, 6, 66, 83, 77, 79, 12, 66, 2, 66, 32, 43, 40, 50, 26, 79, 86, 57, 6, 21, 79, 12, 43, 36 >

You allow mutation of input to interfere with test cases.

My code has passed all of the sample tests but it is failing for the bigger ones. Could you please provide me any suggestions on what to look for? what kinda situations may not be present on the tests cases that are being tested on the bigger cases? By any chance, would you have any big test case that you could share with us? Thank you!