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Nicolas DUBIEN
Nicolas DUBIEN

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Advent of PBT 2021 - Day 14

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

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

/**
 * Re-order multiple tabs at the same time and relatively to others
 * (as browsers do).
 * 
 * In modern browsers including Mozilla Firefox or Google Chrome,
 * users can easily select N non-contiguous tabs at the same time
 * and reorder them in a single move.
 * 
 * For instance if you have the tabs, A, B, C, D and E
 * you can select A and C and move them after D
 * to get B, D, A, C and E.
 *
 * @param tabs - The original set of tabs of the browser
 * @param selectedTabs - The tab currently being moved, a subarray
 *                       of tabs
 * @param moveBeforeTab - One of the tabs oftabs but not of
 *                        selectedTabs taken as a reference
 *                        for the dropping place
 *
 * @returns
 * New tabs configuration after the drop.
 */
export function reorderTabs(
  tabs: number[],
  selectedTabs: number[],
  moveBeforeTab: number
): number[]
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We already wrote some examples based tests for it:

it("should be able to re-order one tab alone", () => {
  // Arrange
  const originalTabs = [0, 1, 2, 3, 4];
  const selectedTabs = [2];
  const moveTabsBefore = 4;

  // Act
  const reordered = reorderTabs(originalTabs, selectedTabs, moveTabsBefore);

  // Assert
  expect(reordered).toEqual([0, 1, 3, 2, 4]);
});

it("should be able to re-order many contiguous tabs", () => {
  // Arrange
  const originalTabs = [0, 1, 2, 3, 4];
  const selectedTabs = [0, 1];
  const moveTabsBefore = 4;

  // Act
  const reordered = reorderTabs(originalTabs, selectedTabs, moveTabsBefore);

  // Assert
  expect(reordered).toEqual([2, 3, 0, 1, 4]);
});

it("should be able to re-order many non-contiguous tabs", () => {
  // Arrange
  const originalTabs = [0, 1, 2, 3, 4];
  const selectedTabs = [0, 2];
  const moveTabsBefore = 4;

  // Act
  const reordered = reorderTabs(originalTabs, selectedTabs, moveTabsBefore);

  // Assert
  expect(reordered).toEqual([1, 3, 0, 2, 4]);
});
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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-14-3g438?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-14-solution-577o


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.

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