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[Proposal] Migrate to fast-check #353

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@dubzzz dubzzz commented Jun 15, 2021

What?
This Pull Request is mostly a proposal to migrate from jsverify to fast-check.

Why?
jsverify's owner stopped the maintenance of the library more than a year ago. In addition, the last real commit to jsverify was on the 6th of September 2019.

Benefits of fast-check over jsverify

  1. You don't need to define unmapping fuctions on your calls to map (smap in jsverify).
  2. The arbitraries are able to find more bugs. For instance if you take a look into the updated tests you'll see that I had to calm down the generator of numbers because it was reporting issues if we used it fully.
  3. There is a built-in way to handle commands. But I did not adapt the tests of LRUCache yet (they can definitely use the builder of commands provided by fast-check).
  4. Maintained.

key: jsc.elements(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h']),
value: jsc.nat,
}) as any
const arbitraryCommand = fc.record({
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There is a built-in way to deal with commands in fast-check. I could probably migrate the test to it.

Comment on lines +7 to +15
let numericType = fc
.double({
next: true,
noDefaultInfinity: true,
noNaN: true,
min: -1 / numericTypeMinAccuracy,
max: 1 / numericTypeMinAccuracy,
})
})
.map(d => Math.round(d / numericTypeMinAccuracy) * numericTypeMinAccuracy)
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Here the arbitrary fc.double was able to find potential issues when used with full resolution. Contrary to jsc.number it can generate any number from -Infinity to +Infinity including -0, Number.MIN_VALUE, Number.EPSILON and others (from small to large values).

Comment on lines +235 to +236
// If the above expect(...) assertion fails, we won't reach here.
return true
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No need for return with fast-check. No return or return true is success. Throw or return false is failure.

@dubzzz dubzzz changed the title Migrate to fast-check [Proposal] Migrate to fast-check Jun 15, 2021
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