Advent of PBT 2021 - Day 9

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

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

/**
 * Build a sorted version of the passed array by relying
 * on "<" comparison.
 *
 * @param tab - Original array to be sorted
 *
 * @returns
 * Sorted copy of the original array.
 */
declare function sorted<T>(tab: T[]): T[];

We already wrote some examples based tests for it:

it("should keep sorted array sorted", () => {
  expect(sorted([1, 2, 3])).toEqual([1, 2, 3]);
});

it("should sort reverse-sorted array", () => {
  expect(sorted([3, 2, 1])).toEqual([1, 2, 3]);
});

it("should sort any array", () => {
  expect(sorted([5, 2, 3, 1, 8])).toEqual([1, 2, 3, 5, 8]);
});

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-9-mxzok?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-9-solution-58dp

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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.