Is there an easy way to stub out time.Now() globally during test?


Part of our code is time sensitive and we need to able to reserve something and then release it in 30-60 seconds etc, which we can just do a time.Sleep(60 * time.Second)

I have just implemented time interface and during test use a stubbed implementation of the time interface, similar to this golang-nuts discussion.

However, time.Now() is called in multiple sites which means we need to pass a variable around to keep track of how much time we have actually slept.

I was wondering if there is an alternative way to stub out time.Now() globally. Maybe making a system call to change the system clock?

Maybe we can write our own time package which basically wraps around the time package but allows us to change it?

Our current implementation works well, I am a go beginner and I am curious to see if anyone has other ideas?


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.


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, less side effects means that it is much easier to make the code run concurrently.

Answered By – nemo

Answer Checked By – Candace Johnson (GoLangFix Volunteer)

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