How to check if a set contains exact values with Jest in JS?

TLDR: With jest-extended package you can write: expect([...set]).toIncludeSameMembers([value1, value2]);. If you are looking to a native, but longer solution scroll down a bit.

Table of contents

    Let's say that you want to create a tic tac toe game solver and need to test if a function that returns possible moves from a given state works properly.

    const state = [
      ['X', 'O', 'X'],
      ['X', 'O', null],
      ['O', null, 'X'],
    ];
    const possibleMoves = new Set();
    possibleMoves.add([
      ['X', 'O', 'X'],
      ['X', 'O', null],
      ['O', 'O', 'X'],
    ]);
    possibleMoves.add([
      ['X', 'O', 'X'],
      ['X', 'O', 'O'],
      ['O', null, 'X'],
    ]);
    const foundPossibleMoves = getPossibleMoves(state, 'O');

    Jest doesn't have a built-in functions for working with a set data structure, but it greatly supports comparing arrays. You can convert set to array and check for inclusion (elements ordering does not matter), but then you also need to check if sets have equal sizes:

    expect([...foundPossibleMoves]).toEqual(
      expect.arrayContaining([...possibleMoves]),
    );
    expect(foundPossibleMoves.size).toEqual(possibleMoves.size);

    Fortunately, jest-extended package contains matcher named toIncludeSameMembers that does the both:

    expect([...foundPossibleMoves]).toIncludeSameMembers([...possibleMoves]);

    Jest performs deep elements comparison, so the check above should pass.

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    Artur Ziętkiewicz
    Artur Ziętkiewicz Elixir& React Developer

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