Try something like
github.com/facebookgo/clock
On Thursday, 28 January 2021 at 21:15:50 UTC Christian Worm Mortensen wrote:
> Hi!
>
> Suppose I want to unit test this function:
>
> func generator() <-chan int {
> ret := make(chan int)
> go func() {
> for i := 0; i < 10; i++ {
> ret <- i
> time.Sleep(time.Second)
> }
> }()
> return ret
> }
>
> What is a good way to do that? One way is to do it is like this:
>
> func testGenerator() {
> start := time.Now()
> g := generator()
> for i := 0; i < 10; i++ {
> v := <-g
> if v != i {
> panic("Wrong value")
> }
> }
> elapsed := time.Now().Sub(start)
> if elapsed < 9*time.Second || elapsed > 11*time.Second {
> panic("Wrong execution time")
> }
> }
>
> However there are several issues with this:
>
> 1) The unit test takes a long time to run - 10 seconds.
> 2) The unit test is fragile to fluctuations in CPU availability
> 3) The unit test is not very accurate
>
> Of course this is a simple example. But what if I want to test a
> complicated piece of code with many go routines interacting in complicated
> ways and with long timeouts?
>
> In other programming languages, I have been able to implement a form of
> virtual time which increases only when all threads are waiting for time to
> increase. This allows functions like generator above to be tested basically
> instantly and this has been extremely useful for me in many projects over
> the years.
>
> Can I do something similar in Go? I would expect I would need to wrap
> time.Now, time.Sleep and time.After which I will be happy to do.
>
> I can see that Go has a deadlock detector. If somehow it was possible to
> have Go start a new Go routine when a deadlock was detected, I think it
> would be pretty straight forward to implement virtual time as described. I
> could then do something like:
>
> runtime.registerDeadlockCallback(func () {
> // Increase virtual time and by that:
> // * Make one or more wrapped time.Sleep calls return or
> // * Write to one or more channels returned by wrapped time.After.
> })
>
> Obviously this would only be needed for test code, not production code.
>
> Thanks,
>
> Christian
>
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