auto date = Date.init;
date.dayOfGregorianCal = 1;
assert(date == Date(1, 1, 1));

date.dayOfGregorianCal = 365;
assert(date == Date(1, 12, 31));

date.dayOfGregorianCal = 366;
assert(date == Date(2, 1, 1));

date.dayOfGregorianCal = 0;
assert(date == Date(0, 12, 31));

date.dayOfGregorianCal = -365;
assert(date == Date(-0, 1, 1));

date.dayOfGregorianCal = -366;
assert(date == Date(-1, 12, 31));

date.dayOfGregorianCal = 730_120;
assert(date == Date(2000, 1, 1));

date.dayOfGregorianCal = 734_137;
assert(date == Date(2010, 12, 31));