With seed as cli parameter

[raphael-proust]

This PR adds a CLI parameter (-s/--seed) to make the quickcheck mode fully deterministic.

Note that the current state is mostly deterministic: two consecutive runs derive the same original seed from the global Random PRNG. However, linked libraries can change the PRNG state:

• A linked library may be calling Random.self_init which makes the tests non-deterministic.
• Updating a dependency may introduce or remove calls to Random.int, changing the determinism.

This PR is not yet tested. I wanted to get a quick mood check before putting significant effort in: Is this change or one like it likely to be merged? Is there interest for such a feature? Any comments on the user interface?

[stedolan]

Sounds good to me!

[raphael-proust]

:+1: I'll test this, make necessary corrections and update this PR.

[raphael-proust]

Good news: the seed flag works.

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I also added a --repeat flag to set the number of repetitions in quickcheck mode. It also works.

It's not quite redundant with the infinity mode, but it's also not orthogonal. So I'm happy to either remove it, merge both options into a single option (maybe -r 0 can mean infinite?), or make some other changes.

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By the way, I found out that it works by finding that the test_calendar actually fails:

$ ./_build/default/examples/calendar/test_calendar.exe -s 0
calendar: ....
calendar: PASS
$ ./_build/default/examples/calendar/test_calendar.exe -s 0 -r 50000
calendar: ....
calendar: FAIL

When given the input:

    [1899-08-31 14:14:45; 1900-07-10 00:40:53]

the test failed:

    1900-07-11 00:40:53 != 1900-07-10 00:40:53

[raphael-proust]

bump

[raphael-proust]

ping

[stedolan]

Merged! Thanks, and apologies for forgetting about this.