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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