github.com/vimeo/go-clocks

go-clocks provides a modern context-aware clock interface

When writing code that involves time, it is not uncommon to want control over the flow of that resource (particularly for tests). Many applications end up storing a field called now and of type func() time.Time, to mock out time.Now(), but that only covers a fraction of the time package's interface, and only covers the most trivial cases.

The Clock interface in go-clocks covers both querying and waiting for time. Querying is handled via Clock.Now() and Clock.Until() while waiting is handled by Clock.SleepFor() and Clock.SleepUntil().

Using Clock

Generally, it is recommended store a field of type Clock in struct-types that might need to interact with time. In production, one should use DefaultClock(), while in tests, one will generally want some combination of fake.Clock and offset.Clock.

fake.Clock and tests

While Clock is a nice interface with both context-aware Clock.SleepFor() and Clock.SleepUntil(), it really shines when combined with the fake.Clock in this repository's fake subpackage.

fake.Clock has a number of methods for doing implicit synchronization based on the number of instances of SleepFor/SleepUntil waiting on a particular fake.Clock instance.

offset.Clock and tests

A significantly simpler Clock implementation lives in the offset subpackage in the form of the offset.Clock type, which adds a constant offset to a wrapped Clock. This is useful for simulating clock-skew between different components within a test without having to do extra bookkeeping associated with multiple fake.Clocks.

Dependencies

go-clocks very deliberately has zero dependencies aside from the Go standard library.

Test coverage

As of the v1.0.0 release of go-clocks, the package has 100% test statement-based coverage as measured by go test -cover in all three packages. We endeavor to keep it that way.