I think it might be good to add a test for an n for which xk is not n - 1, such as 10, 12 or 14.

The below error message is inconsistent with specifications. Either specification is incomplete or test are incorrect.

Wrong value for Joshua,Harper,Grace,Isabella,Mason,Ethan,David - Expected: ["Grace","Harper","Joshua"], instead got: ["David","Ethan","Grace","Harper","Isabella","Joshua","Mason"]

Wrong value for Brooklyn,David,Anthony,Grace,Alexander,Andrew,Mason,Anthony,Addison,Emma,Robert,Mason,Emily,Elijah,Robert,Angel,Michael - Expected: ["Anthony","Brooklyn","David"], instead got: ["Addison","Alexander","Andrew","Angel","Anthony","Anthony","Brooklyn","David","Elijah","Emily","Emma","Grace","Mason","Mason","Michael","Robert","Robert"]

Points should be zero after new ratings are calculated.
"gains of loss" should be "gains or losses"

If n = -7, should the answer be -5 or -10?