Advent of PBT 2021 - Day 17

Advent of PBT 2021 — Learn how to use property based testing and fast-check through examples

Our algorithm today is: isHumbleNumber.
It comes with the following documentation and prototype:

/**
 * Check if a number is an Humber number.
 *
 * Humble numbers are positive integers which have
 * no prime factors > 7.
 *
 * Source: https://rosettacode.org/wiki/Humble_numbers
 *
 * @param n - The number to be checked,
 *            superior or equal to zero and up to 2**31 -1
 */
declare function isHumbleNumber(n: number): boolean;

We already wrote some examples based tests for it:

it("should consider any prime number <=7 as humble", () => {
  expect(isHumbleNumber(2)).toBe(true);
  expect(isHumbleNumber(3)).toBe(true);
  expect(isHumbleNumber(5)).toBe(true);
  expect(isHumbleNumber(7)).toBe(true);
});

it("should consider any number <=7 as humble", () => {
  expect(isHumbleNumber(0)).toBe(true);
  expect(isHumbleNumber(1)).toBe(true);
  expect(isHumbleNumber(4)).toBe(true);
  expect(isHumbleNumber(6)).toBe(true);
});

it("should consider any compositite of 2, 3, 5 or 7 as humble", () => {
  expect(isHumbleNumber(2 * 2 * 2 * 2 * 2)).toBe(true);
  expect(isHumbleNumber(2 * 2 * 3 * 3 * 5 * 5 * 7 * 7)).toBe(true);
});

it("should consider number with prime factor >7 as non-humble", () => {
  expect(isHumbleNumber(11)).toBe(false);
  expect(isHumbleNumber(2 * 11)).toBe(false);
});

How would you cover it with Property Based Tests?

In order to ease your task we provide you with an already setup CodeSandbox, with examples based tests already written and a possible implementation of the algorithm: https://codesandbox.io/s/advent-of-pbt-day-17-qvdwh?file=/src/index.spec.ts&previewwindow=tests

You wanna see the solution? Here is the set of properties I came with to cover today's algorithm: https://dev.to/dubzzz/advent-of-pbt-2021-day-17-solution-3gfe

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Back to "Advent of PBT 2021" to see topics covered during the other days and their solutions.

More about this serie on @ndubien or with the hashtag #AdventOfPBT.