Avoid side effect when unit testing with Jasmine - node.js

Question

I'm trying to unit test the function below with the testing library node-jasmine:
joinGame(participant) {
console.log('Joining game', participant);
if (this.getParticipants().length >= MAX_NUMBER_OF_PARTICIPANTS) {
throw new Error(`The game with id ${this.getId()} has reached the maximum amount of participants, ${MAX_NUMBER_OF_PARTICIPANTS}`);
}
this.addParticipant(participant);
this.incrementPlayerCount();
this.emit(actions.GAME_JOINED, participant);
// Is the game ready to start?
if (this.playerCount >= REQUIRED_NUMBER_OF_PARTICIPANTS) {
// Start game loop by initializing the first round
this.createRound();
}
}
However, when unit testing the function, a couple of code paths lead me toward calling 'this.createRound()' located at the end of the function. createRound() basically initializes the game loop, start timers, and other side effects completely unrelated to the function I'm unit testing. Look at the test below:
it('should throw an error if a user tries to join a game with the maximum amount of participants has been reached', () => {
game = new Game();
// To test whenever there are two participants in the game
game.joinGame(hostParticipant);
game.joinGame(clientParticipant);
function testJoin() {
game.joinGame(joiningParticipant);
}
expect(testJoin).toThrow();
});
Now when I run the test the test will against my will invoke 'createRound()'. 'createRound()' instantiates a Round instance and starts a countdown timer, which makes the 'npm test' call in my commandline to never finish. Since the test thinks it's apart of the test.
Below is a number of approaches I've thought of and implemented. Although, I don't feel like any of them are "clean", that's why I'm looking for your input.
Approach 1: Stub 'createRound()' inside of the test to replace its functionality. This works fine, but is it the correct way to avoid invoking side effects?
Approach 2: Try setting up/tearing down the Game instance on beforeEach/afterEach. I've tried this approach to no success. By setting the game instance to null on 'afterEach()', however, the instantiated round instance keeps going along with its timer.
Approach 3: Use dependency injection when invoking 'joinGame()' and supply a Round instance. This doesn't make much sense though, because it shouldn't be the client's responsibility of supplying a fresh round instance when invoking 'joinGame()'. Furthermore, not every call to 'joinGame()' invokes 'createRound()'; only when the player counts exceeds the required amount of players.

Answer 1

Stubbing createRound certainly makes sense. You're writing a test to assert behavior of denying a user to join a full game, not whether the timer works as expected. This gets a little hairy if you're stubbing a method on the object under test, but then I would argue that perhaps the logic that manages the timer belongs in it's own separate object.
Of course, you can also consider:
Approach 4: Mock the clocks as described in the jasmine documentation. Assuming the timers rely on setTimeout/setInterval, you can install the fake clock before calling the function, and manually tick the clock to get states on which you can make assertions.