One way to do this is have an internal implementation like func generatorImpl(sleep func(time.Duration)) <-chan int and func generator just calls that one with time.Sleep. Tests are done against generatorImpl where you know have detailed control of how much (typically none) time is actually slept.
Expiration of cookies is tested in that way, see e.g. https://golang.org/src/net/http/cookiejar/jar.go#L159 So while technically Jar.Cookies is never tested the risk is basically nil. V. On Thursday, 28 January 2021 at 22:15:50 UTC+1 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 > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/e5d01e49-7432-453c-a2d9-e17fac1639dan%40googlegroups.com.
