Advent of PBT 2021 - Day 6

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

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

type Fraction = { numerator: number; denominator: number };

/**
 * Simplify a fraction by reducing (if possible) the numerator
 * and denominator
 *
 * @param f - Fraction to be simplified
 *
 * @returns
 * An equivalent fraction with possibly smaller values for numerator
 * and denominator. Additionally only the numerator should be
 * negative after simplification.
 */
declare function simplifyFraction(f: Fraction): Fraction;

We already wrote some examples based tests for it:

it("should simplify the fraction when numerator is divisible by denominator", () => {
  const out = simplifyFraction({ numerator: 10, denominator: 5 });
  expect(out).toEqual({ numerator: 2, denominator: 1 });
});

it("should simplify the fraction when numerator and denominator have a shared dividor", () => {
  const out = simplifyFraction({ numerator: 4, denominator: 10 });
  expect(out).toEqual({ numerator: 2, denominator: 5 });
});

it("should not simplify when fraction cannot be simplified", () => {
  const out = simplifyFraction({ numerator: 4, denominator: 9 });
  expect(out).toEqual({ numerator: 4, denominator: 9 });
});

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-6-ijhun?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-6-solution-f7n

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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.