That would certainly be a nice feature!

It would require re-working the main QuickCheck loop in Test.QuickCheck.Test to spawn several tests and collect the reults. Possibly a bit of work, but something we probably ought to do.

@amigalemming Just as a side note, it is possible to show progress information, even when running QuickCheck properties in parallel. hspec does exactly that.

The hairy details:

• We assume that the user runs a test suite with n tests.
• The user specifies N, the number of parallel tests to run at a time.
• Hspec's runner spawns one thread for each test, t₁ to tₙ.
• Each thread tₓ has an associated Mₓ :: MVar (Either Progress Result).
• Each thread waits on a semaphore with the capacity N.
• Once a thread tₓ is signaled to run, it runs the associated test; while doing so it writes progress information into Mₓ and once it's done the result (that is write if the MVar is empty, otherwise replace).
• The applications main thread folds over the list M₁..ₙ
• For each Mₓ it reads the current value and writes progress information as long as it gets a Left-value.
• Once it reads a Right-value it reports the result to the user and moves on to Mₓ₊₁.

With this approach we see progress information for the currently running test with the lowest x only. In practice this works out nicely.

/cc @feuerbach

It seems that QuickCheck-2.11 uses more cores, at least top reports CPU usage higher than 300%. If so, I think it is not a good idea to parallelize without permission by the user. How can I limit the number of cores/threads used?

No, it doesn't parallelise automatically! Not sure what's going on there.

I have implemented this :) With some blood, sweat, and tears, it should be in 2.16. Stay tuned

How soon 2.16 is expected? If it's "soon", than I won't care updating to QuickCheck-2.15 at all in between.

@phadej There is no timeline. I think it will be a nightmare to merge, but worth it.

To clarify; I would not wait if I were you.

Here is a link to the paper describing the work done on this: https://arxiv.org/pdf/2404.16062