The four rules, one example year each

All 6 scenarios hold

Yes/No in the expectation column is read by a custom type converter.

expected outcome broken scenario
ScenarioYearIs Leap Year?
Not divisible by 42001No
Divisible by 42004Yes
Divisible by 100 but not by 4002100No
Divisible by 4002000Yes
Year zero0Yes
A year before the common era-1No