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Nicolas DUBIEN
Nicolas DUBIEN

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Advent of PBT 2021 - Day 5

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

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

 * You're given a message where spaces have been removed.
 * Your aim is to find back the original message given a dictionary
 * containing all the words. As many messages could be encoded the
 * same way, you may have to return two or more messages. No specific
 * ordering is expected when multiple solutions are available but all
 * must be returned.
 * @param spacelessMessage - Message without any spaces
 * @param words - List of accepted words (no repeat and at least one
 * character long)
 * @returns
 * All the possible messages made only with the received words that
 * could have led to this spacelessMessage.
declare function respace(spacelessMessage: string, words: string[]): string[];
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We already wrote some examples based tests for it:

it("should be able to detect one match when there is only one", () => {
  const out = respace("helloworld", ["hello", "world"]);
  expect(out).toEqual(["hello world"]);

it("should not detect any match and produce empty arrays when no matchs", () => {
  const out = respace("hellowooorld", ["hello", "world"]);

it("should be able to detect all the matches when multiple are eligible", () => {
  const out = respace("tititi", ["ti", "titi"]);
  expect(sorted(out)).toEqual(["ti ti ti", "ti titi", "titi ti"]);
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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:

You wanna see the solution? Here is the set of properties I came with to cover today's algorithm:

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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