With implementing a custom interface you are already on the right way. I take it you use the following advise from the golang-nuts thread you’ve posted:
type Clock interface {
Now() time.Time
After(d time.Duration) <-chan time.Time
}
and provide a concrete implementation
type realClock struct{}
func (realClock) Now() time.Time { return time.Now() }
func (realClock) After(d time.Duration) <-chan time.Time { return time.After(d) }
and a testing implementation.
Original
Changing the system time while making tests (or in general) is a bad idea.
You don’t know what depends on the system time while executing tests and you don’t want to find out the hard way by spending days of debugging into that. Just don’t do it.
There is also no way to shadow the time package globally and doing that would not do
anything more you couldn’t do with the interface solution. You can write your own time package
which uses the standard library and provides a function to switch to a mock time library for
testing if it is the time object you need to pass around with the interface solution that is bothering you.
The best way to design and test your code would probably be to make as much code stateless as possible.
Split your functionality in testable, stateless parts. Testing these components separately is much easier then. Also, fewer side effects means that it is much easier to make the code run concurrently.