Advent of PBT 2021 - Day 12

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

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

/**
 * Given a string s containing just the characters '(', ')', '{',
 * '}', '[' and ']', determine if the input string is valid.
 *
 * @param expression -
 *
 * @returns
 * An input string is valid if:
 * Open brackets must be closed by the same type of brackets.
 * Open brackets must be closed in the correct order.
 */
declare function validParentheses(expression: string): boolean;

We already wrote some examples based tests for it:

it("should accept simple expressions", () => {
  expect(validParentheses("[]")).toBe(true);
});

it("should accept nested expressions", () => {
  expect(validParentheses("[({})]")).toBe(true);
});

it("should accept expressions with multiple groups", () => {
  expect(validParentheses("[({})][]([])")).toBe(true);
});

it("should reject wrong matching bracket", () => {
  expect(validParentheses("[)")).toBe(false);
});

it("should reject unbalanced brackets with more closing", () => {
  expect(validParentheses("[]()}")).toBe(false);
});

it("should reject unbalanced brackets with more opening", () => {
  expect(validParentheses("[](){")).toBe(false);
});

it("should reject bad nesting", () => {
  expect(validParentheses("[(])")).toBe(false);
});

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-12-fjifg?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-12-solution-3oic

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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.