Utilities for working with time.
Clock provides points in time relative to the current point in time, for
example: now, 2 days ago, 4 weeks from now, etc. For tesability, use Clock
rather than other ways of accessing time, like
new DateTime(), so that you
can use a fake time function in your tests to control time.
aWeek are unit duration constants to allow writing for example:
const Duration(days: 1)
aSecond * 30vs.
const Duration(seconds: 30)