Property-based testing support in bun:test (fast-check integration, or Bun's own take)

[LewisAlderman]

I use fast-check for property-based testing and would love to run it through bun test properly. Vitest and Jest both have official integrations (@fast-check/vitest, @fast-check/jest) that add test.prop([...arbitraries])('name', fn). Neither works with bun:test, and fast-check's docs say there's no Bun connector, which is why I'm writing this.

Calling fc.assert(fc.property(...)) inside a normal test() works fine today, so nothing is blocked. The gaps are the things only a test runner can do:

• bun test --seed shuffles test order but doesn't reach fast-check, so one seed can't reproduce a whole run.
• The default 5s timeout can kill a property halfway through shrinking, and then you lose the minimal counterexample unless you set interruptAfterTimeLimit yourself.
• Failing seeds and counterexamples only show up in error text. Bun can't save them, replay them on the next run, or put them in a JUnit report.

I don't have strong opinions on the shape. It could be test.prop built on fast-check as a peer dependency, maybe using the plugin API fast-check added in 4.10. Or Bun could build its own version, which might allow things a library can't do, like using JSC's coverage data to guide which inputs get generated.

In theory you could get most of the way there with a small prop() wrapper around fc.assert plus fc.configureGlobal in a preload file, or by running Vitest under Bun instead. Both would work, but neither can do the runner-level parts above.

Curious whether this is something the team would consider.