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

Question

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?

Answer 1

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

Answer 2

If the methods you need to mock are few, such as Now(), you can make a package variable which can be overwritten by tests:

package foo  import "time"  var Now = time.Now  // The rest of your code...which calls Now() instead of time.Now() 

then in your test file:

package foo  import (     "testing"     "time" )  var Now = func() time.Time { return ... }  // Your tests