What is the sequence in which Jest executes its tests?

A fascinating challenge I've taken on involves testing a card game created in JavaScript using Jest.

Currently, I have developed two tests: one to verify the creation of a 52-card deck and another to confirm that the player is dealt two cards at the beginning of the game:

const { Deck, Player} = require("./cardgame")
let deck = new Deck()
deck = deck.createDeck()
let player = new Player()
player.openinghand(deck)

test('Expecting the Deck to contain 52 cards', () => {
    expect(deck.length).toBe(52);
});

test('Expecting the opening hand of the player to consist of 2 cards', () => {
    expect(player.hand.length).toBe(2)
});

Upon running the tests, only the second one passes. The failure of the first test can be attributed to the fact that the deck length does not remain at 52 throughout the process. Does Jest execute all tests simultaneously rather than in the order they are written? How can I adjust my approach to ensure both tests pass successfully?

Answer №1

It is important for unit tests to be idempotent, meaning that the result should remain consistent regardless of how many times or in what order they are executed.

Ensuring that the test environment, test double, and test data are all independent for each test case is crucial.

Your code suggests that these two test cases may share the same test data, which poses a risk of one test case inadvertently affecting another.

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