@informalsystems/quint/test/rng.test.ts

Core tool for the Quint specification language

import { describe, it } from 'mocha'
import { assert, expect } from 'chai'

import { Rng, newRng } from '../src/rng'

function testForRange(rng: Rng, bound: bigint, nsamples: number) {
  for (let i = 0; i < nsamples; i++) {
    const state = rng.getState()
    const v = rng.next(bound)
    assert(0n <= v && v < bound, `${v} is not in the range [0, ${bound}), state = ${state}`)
  }
}

describe('rng', () => {
  it('produces an expected sequence', () => {
    const rng = newRng(20230404n)
    expect(rng.next(1000n)).to.equal(314n)
    expect(rng.next(2000n)).to.equal(103n)
    expect(rng.next(3000n)).to.equal(1254n)
    expect(rng.next(2n ** 256n)).to.equal(
      39968831094728793095337668312741798650168913551481632943502796831606193252535n
    )
  })

  it('produces big integers in [0, 10000)', () => {
    testForRange(newRng(), 10000n, 100000)
  })

  it('produces big integers in [0, 2^16)', () => {
    testForRange(newRng(), 2n ** 16n, 10000)
  })

  it('produces big integers in [0, 2^32)', () => {
    testForRange(newRng(), 2n ** 32n, 10000)
  })

  it('produces big integers in [0, 2^32 + 1))', () => {
    testForRange(newRng(), 2n ** 32n + 1n, 10000)
  })

  it('produces big integers in [0, 2^64))', () => {
    testForRange(newRng(), 2n ** 64n, 10000)
  })

  it('produces big integers in [0, 2^64 + 1))', () => {
    testForRange(newRng(), 2n ** 64n + 1n, 10000)
  })

  it('produces big integers in [0, over 2^64))', () => {
    testForRange(newRng(), 2n ** 64n + 3n * 5n * 7n * 11n, 10000)
  })

  it('produces big integers in [0, 2^96 + 1))', () => {
    testForRange(newRng(), 2n ** 96n + 1n, 10000)
  })

  it('produces big integers in [0, over 2^96))', () => {
    testForRange(newRng(), 2n ** 96n + 3n * 5n * 7n * 11n, 10000)
  })

  it('produces big integers in [0, over 2^256))', () => {
    testForRange(newRng(), 2n ** 256n + 2n ** 33n + 11n, 10000)
  })
})