jsverify VS guide.elm-lang.org

Libraries like JSVerify or Fast-Check offer essential tools to facilitate property-based testing.

I tend to use anything that offers property-testing, since tests are much shorter to write and uncover lots more hidden assumptions.

My go-to choices per language are:

- Python: Hypothesis https://hypothesis.readthedocs.io/en/latest (also compatible with PyTest)

- Scala: ScalaCheck https://scalacheck.org (also compatible with ScalaTest)

- Javascript/Typescript: JSVerify https://jsverify.github.io

- Haskell: LazySmallCheck2012 https://github.com/UoYCS-plasma/LazySmallCheck2012/blob/mast...

- When I wrote PHP (over a decade ago) there was no decent property-based test framework, so I cobbled one together https://github.com/Warbo/php-easycheck

All of the above use the same basic setup: tests can make universally-quantified statements (e.g. "for all (x: Int), foo(x) == foo(foo(x))"), then the framework checks that statement for a bunch of different inputs.

Most property-checking frameworks generate data randomly (with more or less sophistication). The Haskell ecosystem is more interesting:

- QuickCheck was one of the first property-testing frameworks, using random genrators.

- SmallCheck came later, which enumerates data instead (e.g. testing a Float might use 0, 1, -1, 2, -2, 0.5, -0.5, etc.). That's cute, but QuickCheck tends to exercise more code paths with each input.

- LazySmallCheck builds up test data on-demand, using Haskell's pervasive laziness. Tests are run with an error as input: if they pass, we're done; if they fail, we're done; if they trigger the error, they're run again with slightly more-defined inputs. For example, if the input is supposed to be a list, we try again with the two forms of list: empty and "cons" (the arguments to cons are both errors, to begin with). This exercises even more code paths for each input.

- LazySmallCheck2012 is a more versatile "update" to LazySmallCheck; in particular, it's able to generate functions.

The usage of hypothesis is very intuitive and simple, and presents the concept of property-based testing perfectly. So I also wanted to find an equivalent alternative in Node. Two of them have high star ratings on Github, JSVerify with 1.6K stars and fast-check with 2.8K stars. So I took some time to study fast-check a little bit and try to get closer to my daily work.

Systems I've used for this include https://agda.readthedocs.io/en/v2.6.0.1/getting-started/what... https://coq.inria.fr https://www.idris-lang.org and https://isabelle.in.tum.de

An easier alternative is to try disproving the statement, by executing it on thousands of examples and seeing if any fail. That gives us less confidence than a full proof, but can still be better than traditional "there exists" tests. This is called property checking or property-based testing. Systems I've used for this include https://hypothesis.works https://hackage.haskell.org/package/QuickCheck https://scalacheck.org and https://jsverify.github.io

Using create-react-app, you’ll run npm test which uses Jest internally. If you are dealing with a lot of data on the UI, or using TypeScript, use JSVerify for property tests. For end to end tests, Cypress is a great choice.

If you look at the repo for that guide (https://github.com/evancz/guide.elm-lang.org), the description and README clearly state that this is his book on learning Elm, so for me it makes complete sense that it is in the I-form. Maybe the fact that it's linked from the official Elm page without any mention of that causes a feeling of disconnect for you.

An Introduction to Elm (HTML)

I am continually perplexed how poor the official documentation is for Elm (https://guide.elm-lang.org). I love the language, I really enjoy working with it, but where does one go to see the complete API? In particular right now I'm trying to find more on setting various events and accessibility attributes in forms, and this is all I see on the official docs: https://guide.elm-lang.org/architecture/forms.html. Not even a label example on a form page? How is this considered good documentation for a language that has been around for a decade? Is there some secret handshake I need to learn to get access to more in-depth documentation of the language?

I think a good first step would be getting familiar with functional programming in general. I recommend working through the Elm Guide, which will get you acquainted with functional programming idioms and working with immutable data. Then, move on to an introductory Haskell resources, such as Write Yourself a Scheme in 48 Hours. After that, hit up CodeWars and start solving puzzles in Haskell.

I think The Elm Guide does a very good job.

Check out Elm. Page 4 of the intro guide I linked offers something close, which you could build upon to create what you want there.

My advice is to follow the elm official guide. Anyway, any doubt you may have, ping me (gabber) on Elm official slack or write to #beginners channel!

This guide will help you learn and migrate to Elm with assumption you already know the basics of React. The Elm guide is great and will give you a thorough understanding of everything you need to know, in a good order.

Elm Introduction: https://guide.elm-lang.org/

The official Elm guide