quickcheck | Automated property based testing for Rust

A possible solution is pkgs.myHaskellPackages.server.getBuildInputs.haskellBuildInputs, or pkgs.myHaskellPackages.server.getCabalDeps.libraryHaskellDepends.

You can explore these attributes, or any expression, with nix repl. You may have to expose some values from your let bindings though. In this case I just browsed through haskellPackages.warp in nix repl .

I also noticed you use rec in an overlay. This will work for you until it doesn't. I'd recommend to remove rec to avoid accessing attributes in a third way and use the more standard haskellPackagesNew.servant instead.

I think I figured this out, I used this:

This is a syntactic restriction in service of the scoping rules of a where block. Within a where block, values bound in a pattern match are in scope, and values defined in the where block are in scope for guards within that pattern match. As such, a where block must be attached to locations where a pattern match and guards at the very least could exist. This ends up being value declarations and branches of case expressions. In your second example you are trying to attach a where block to an arbitrary expression, which is just not what they're intended to do.

A bunch of these types are implemented in the package quickcheck-instances. Just add that into your dependencies, import Test.QuickCheck.Instances.Natural, and you should be good to go!

tl;dr That is the wrong trait to implement if you want to generate random values of your own type.

The trait Rng is an extension trait for RngCore, with a blanket implementation included. This means that all types which implement RngCore already implement Rng, and you should not try to provide it yourself. Once Rng is put into scope, all implementations of RngCore will have the extra methods provided there.

However:

I want to implement the traits because I later want to use the quickcheck::Arbitrary with my type.

So this is an XY problem! RngCore is designed to create random number generation algorithms, not to define how data types are sampled from a random number source.

Your Arbitrary instance for a Rank contains an Int:

There are several issues with prop_search. While the compiler messages in Haskell can be a bit daunting, the first troubleshooting tip is to realise that (unless you're using some advanced extensions to the language) the type annotations are redundant. The compiler doesn't need the type annotation, but it's good practice to include them because it helps with readability.

Thus, first try to see if the expression itself compiles. Here, I'm just using GHCi:

Since you haven't yet received an answer for "junit-quickcheck" I can at least confirm that it works as expected in jqwik.net (an alternative to junit-quickcheck using the JUnit 5 platform):

What you want to do is use the Arbitrary instance for a. I can tell you know you need to do this because you already added Arbitrary a as a constraint to the instance, but you need to actually use it. For instance: