Random test generation is flawed; they keep generating wrong results for huge tests and even with reduced board size (like 5x5) they keep generating wrong expected values, albeit more rarely:

XBZBK
FHBAP
XBEJH
TFLJO
EBQYG
expected:<2> but was:<3>

• Tests generate warnings
• Splitting a collection into chunks is a duplicate, and trivial/map/filter is not a novel idea - I don't think combining these 2 into a single kata makes it interesting

If October 23, 2019 was Rebo Wage (Note you have it spelled Rebu in the description) then wouldn't October 22, 2019 (the day before) be Selasa Pon (1 earlier on bothe lists)?

If so, then the sample tests are wrong:

assertEquals("Selasa Kliwon", Weton.getWeton("October 22, 2019"));

The date strings specified in the description does not mention that the numeric months and days are single-digit ones (which is an important distinction).