StreamData: data generation and property testing for Elixir

[tmbb]

@whatyouhide

which as I mention in the README is really Clojure’s test.check approach, credit where credit is due

I’ve read the blog post about test.check by the author. It does look more more less equivalent to what Hypothesis does if you squint a little.

@whatyouhide

The seed that generators accept as argument can be “split”, meaning we can get two seeds from one seed in a deterministic way. So generators just split seeds when they need to pass down the seed. Since everything is deterministic, to “replay” a run you can just pass the same seed (this is already done to integrate with ExUnit where we use ExUnit’s seed).

Well, a seed is even easier to serialize than the Hypothesis byte streams. With a way to serialize text data, you could (and should) save the examples that falsify the tests, so that they could be tested in a next run. And also do other cool things that depend on having serializeable examples.

@whatyouhide

Whether it’s the right API or not, it’s a different discussion

I think you hsould shrink the examples as much as possible, and that includes shrinking <<16, 16>> to <<0>>… I’ll open an issue tomorrow.

@whatyouhide

The values are completely random but the testing is driven by a “generation size” (mentioned in the docs) which guarantees we start with smaller values which makes the chance of an empty list very very high

Well, if including specific examples would complicate the code too much, then merely a high probability might be acceptable, especially if combined with a database of failed examples.

Nice job with the library!