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What's new in fast-check 4.0.0?

· 6 min read
Nicolas Dubien
Nicolas Dubien
fast-check maintainer

The release of fast-check 4.0.0 marks the end of the 3.x series. With this new version, we've streamlined and refined our APIs, embraced modern standards, and removed unnecessary polyfills to enhance performance and maintainability.

Continue reading to explore the detailed updates it brings.

Migration guide​

As with any major release, version 4.0.0 introduces breaking changes. To help ease the transition, we've put together a simplified migration guide that outlines the necessary steps to upgrade incrementally.

If you're currently using v3 and planning to migrate to v4, we highly recommend reviewing our guide for a smooth upgrade process. You can find it here.

Key takeaways​

If I had to summarize this release in three major changes, they would be:

Smarter defaults​

We continue our mission to provide smarter defaults. Whether it's date or object, this release introduces more challenging default behaviors. Our goal is to anticipate potential edge cases for our users, so they can focus on defining their specifications rather than worrying about unexpected issues.

For example, generated dates will now include invalid values by default, and objects may be created without a prototype. While these options remain customizable on a case-by-case basis, our aim is to free users from thinking about potential pitfalls and instead let them concentrate on specifying what they want to achieve.

Unified string builder​

We have consolidated all our string-related arbitraries into a single one: string. Instead of maintaining a variety of separate arbitraries — some focused on characters, others on strings — we now provide a unified approach that handles all string cases.

We postponed the idea of enforcing smarter defaults to strings in v4, but we plan to introduce it in v5. In the meantime, we will work on giving users more powerful ways to override and customize fast-check’s defaults at the arbitrary level.

Finer scheduler​

We've improved our scheduling capabilities to be more precise, ensuring that tasks are only scheduled if they were present at the expected time. This change makes the behavior more predictable and easier to understand from an external perspective.

Looking ahead, we plan to introduce more configuration options in upcoming minor releases. This will allow users to fine-tune the behavior, including the ability to relax constraints on microtasks and other tasks as needed.

Changelog since 3.23.2​

The version 4.0.0 is based on version 3.23.2.

Breaking changes​

  • (PR#5589) Include invalid dates by default
  • (PR#5590) Error with cause by default
  • (PR#5597) Include null-prototype by default in record
  • (PR#5603) Shorter stringified values for null-prototype
  • (PR#5609) Include null-prototype by default in dictionary
  • (PR#5610) Drop deprecated .noBias
  • (PR#5611) Drop deprecated uuidV arbitrary
  • (PR#5613) Drop deprecated unicodeJson* arbitraries
  • (PR#5633) Extend uuid to build any know version
  • (PR#5636) Drop deprecated ascii*
  • (PR#5644) Drop deprecated hexa*
  • (PR#5664) Drop deprecated base64
  • (PR#5665) Drop deprecated stringOf
  • (PR#5666) Drop deprecated char16bits and string16bits
  • (PR#5667) Drop deprecated fullUnicode*
  • (PR#5669) Drop deprecated unicode*
  • (PR#5671) Drop deprecated char
  • (PR#5674) Drop deprecated big{U|}int{N|}
  • (PR#5679) Drop method nextArrayInt from Random
  • (PR#5694) Drop deprecated .noShrink
  • (PR#5821) Force usage of Node >=12.17.0

Features​

  • (PR#5577) Better typings for constantFrom
  • (PR#5605) Better typings for constant
  • (PR#5773) Arbitrary<XxxArray> => Arbitrary<XxxArray<ArrayBuffer>>
  • (PR#5783) Simplify types for fc.record

Fixes​

  • (PR#5604) Bug: Better rejection handling in scheduleSequence
  • (PR#5672) Bug: Resist to external poisoning for json
  • (PR#5696) Bug: Stricter checks for consecutive noBias
  • (PR#5608) CI: Clean unhandled rejections in tests for scheduler
  • (PR#5670) CI: Move build chain to ESM
  • (PR#5136) CI: Toggle on isolatedDeclarations flag on the project
  • (PR#5685) CI: Stabilize e2e on bigint and duplicates
  • (PR#5695) CI: Move CI jobs to Node 22
  • (PR#5719) CI: Toggle ON faster documentation build
  • (PR#5742) CI: Fix lock file breakeage
  • (PR#5770) CI: Switch CI commands to node --run
  • (PR#5578) Clean: Remove withDeletedKeys from record
  • (PR#5581) Clean: Enforce run{Before/After}Each on property
  • (PR#5634) Clean: Drop unneeded catch param
  • (PR#5763) Clean: Abide by lint rule no-empty-object-type
  • (PR#5767) Clean: Abide by lint rule no-unused-vars
  • (PR#5803) Clean: Fix lint error in ConstantArbitrary class
  • (PR#5522) Doc: Advent of PBT Day 14
  • (PR#5531) Doc: Do not display success count
  • (PR#5524) Doc: Advent of PBT Day 15
  • (PR#5532) Doc: Stop trimming user inputs for the Advent of PBT
  • (PR#5526) Doc: Advent of PBT Day 16
  • (PR#5527) Doc: Advent of PBT Day 17
  • (PR#5539) Doc: Advent of PBT, Day 18
  • (PR#5542) Doc: Add missing comment sections on Advents
  • (PR#5543) Doc: Add socials illustrations on some Advents
  • (PR#5540) Doc: Advent of PBT, Day 19
  • (PR#5547) Doc: Add comments section on Day 19
  • (PR#5550) Doc: Advent of PBT, Day 20
  • (PR#5551) Doc: Comments section for Day 20
  • (PR#5554) Doc: Make Day 15 compliant to its own spec
  • (PR#5555) Doc: Fix validation of Advent of PBT Day 20
  • (PR#5549) Doc: Advent of PBT, Day 21
  • (PR#5552) Doc: Advent of PBT, Day 22
  • (PR#5557) Doc: Drop useless Advent's calls to counter API
  • (PR#5553) Doc: Advent of PBT, Day 23
  • (PR#5558) Doc: Advent of PBT, Day 24
  • (PR#5564) Doc: Add typespec-fast-check to ecosystem page
  • (PR#5684) Doc: Flag migration guide with WIP
  • (PR#5768) Doc: Document the Unicode version
  • (PR#5774) Doc: Update CONTRIBUTING.md after switch to pnpm
  • (PR#5788) Doc: Add new contributor AlexErrant
  • (PR#5789) Doc: Add "Answering Questions" to gruhn
  • (PR#5795) Doc: Enrich minimal support section
  • (PR#5806) Doc: Fix GitHub workflow badge on README
  • (PR#5805) Doc: Add new contributor ahrjarrett
  • (PR#5814) Doc: Drop direct link to the Advent Of PBT
  • (PR#5583) Performance: Faster property::run with strict equality checks
  • (PR#5584) Performance: Delay computation of Error stack when no cause
  • (PR#5612) Performance: Drop unneeded BigInt check in mixedCase
  • (PR#5614) Performance: Faster scheduling of scheduleSequence
  • (PR#5615) Performance: Speed-up race-condition schedulers
  • (PR#5617) Performance: Faster initialization of globals by dropping typeof checks
  • (PR#5676) Performance: Faster read of parameters passed to runners
  • (PR#5677) Performance: Faster read of constraints on object and related
  • (PR#5618) Performance: Faster rewrite of double
  • (PR#5678) Performance: Faster ipV6 generation with cached string builders
  • (PR#5771) Performance: Mark all arbitraries as side-effect free
  • (PR#5786) Performance: Mark all arbitraries as side-effect free
  • (PR#5787) Performance: Target ES2020 in produced bundle
  • (PR#5600) Refactor: Rewrite of scheduleSequence
  • (PR#5635) Refactor: Switch to object spreading rather than Object.assign
  • (PR#5710) Script: Moving from yarn to pnpm
  • (PR#5815) Script: Add support for pnpm scripts in generate-changelog
  • (PR#5816) Script: Take into account bumps on one part of monorepo for changelogs
  • (PR#5817) Script: Fix call to changesets to generate changelog for v4
  • (PR#5616) Test: Stop checking for BigInt in tests
  • (PR#5673) Test: Cover even more arbitraries within Poisoning
  • (PR#5734) Test: Move website tests to Vitest
  • (PR#5736) Test: Do not scan useless directories for tests on website
  • (PR#5743) Test: Drop useless snapshots results
  • (PR#5756) Test: Fix test in double.spec
  • (PR#5790) Test: Check TypeScript 5.7 to assess it never breaks