## DEV Community

Nicolas DUBIEN

Posted on • Updated on

# Advent of PBT 2021 - Day 10

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

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

``````/**
* Compute the minimal number of changes to be applied onto stringA
* to change it into stringB.
* In other words: Compute the distance of Levenshtein between
* two strings.
*
* @param stringA - The first string to be taken into account
* @param stringB - The second string to be taken into account
*
* @returns
* Minimal number of single-character edits (insertions, deletions or
* substitutions) to be applied onto stringA to change it into
* stringB.
*/
declare function minimalNumberOfChangesToBeOther(
stringA: string,
stringB: string
): number;
``````

We already wrote some examples based tests for it:

``````it("should not consider any change to move to same value", () => {
const out = minimalNumberOfChangesToBeOther("azerty", "azerty");
expect(out).toBe(0);
});

it("should properly handle added characters", () => {
const out = minimalNumberOfChangesToBeOther("azerty", "0aze5rty9");
expect(out).toBe(3); // add: 0, 5, 9
});

it("should properly handle removed characters", () => {
const out = minimalNumberOfChangesToBeOther("0aze5rty9", "azerty");
expect(out).toEqual(3); // remove: 0, 5, 9
});

it("should properly handle updated characters", () => {
const out = minimalNumberOfChangesToBeOther("azerty", "AzERTy");
expect(out).toEqual(4); // update: a->A, e->E, r->R, t->T
});

it("should properly handle mix of add/remove/update", () => {
const out = minimalNumberOfChangesToBeOther("azerty", "0az1eRt");
expect(out).toEqual(4); // add: 0, 1, remove: y, update: r->R
});
``````

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-10-78utw?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-10-solution-3a3d

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