assert(Date(1999, 1, 6).endOfMonth == Date(1999, 1, 31));
assert(Date(1999, 2, 7).endOfMonth == Date(1999, 2, 28));
assert(Date(2000, 2, 7).endOfMonth == Date(2000, 2, 29));
assert(Date(2000, 6, 4).endOfMonth == Date(2000, 6, 30));