JSVerify vs scalaprops

JSVerify is a free, open-source property-based testing library for JavaScript, inspired by QuickCheck. It generates inputs and checks whether a stated property holds across them. When a check fails, it attempts to shrink the generated input into a smaller counterexample. Properties can return Promises, allowing asynchronous methods to be tested. JSVerify is framework agnostic; the project names Mocha, nodeunit, and Jasmine as examples. The README instructs users to install it with `npm install jsverify` and says TypeScript typings are provided, though TypeScript specs cannot use the type DSL. Documented defaults are 100 tests and a maximum generated-value size of 50. Options cover test count, maximum generated size, quiet output, and random generator state. Generated values are deterministic when using primitives from the random module, and the RNG state can be set. The project is maintained by phadej and licensed under MIT. Its official site points to the GitHub README for API and usage documentation. The README cautions that exposed utility functions may change incompatibly, including in patch releases.

Scalaprops is a free Scala property-based testing library for Linux. It generates test data, including non-constant scala.FunctionN values through Cogen, and lets each test define flexible parameters. Law checking is configurable, with identifiers that may use types other than String. Scalaz integration supplies laws plus Gen and Cogen instances for Scalaz types. Randomness uses an immutable generator rather than mutable scala.util.Random. Failed tests report their starting seed, which can be passed again with --seed= for repeatable runs. The README states support for Scala.js and Scala Native, using Mersenne Twister by default on JVM and Scala Native and Tiny Mersenne Twister on Scala.js. An sbt plugin adds scalapropsOnly selection by test class, method, and parameter. ScalapropsFramework and sbt are listed test runners. Parallel test execution is unsupported.