CODEWITHSUNDEEP
javascripttypescripttestingts-jestjavascript-inheritance
raghuveer ambedkar
raghuveer ambedkar

Reputation: 79

Unit testing private methods and event listeners in TypeScript class hierarchy

I'm new to writing unit tests for private methods and I've been researching how to approach this in TypeScript. However, I couldn't find a solution that fits my scenario.

Here's a simplified version of my TypeScript code:

export class CallbackManager {
   protected queue: Set<() => void>;
   constructor() {
        this.queue = new Set();
   }
}

export class Report extends CallbackManager {
   public addToQueue(publishMetric: () => void): void {
        this.queue.add(publishMetric);
   }

   private flushQueue(): void {
        if (this.queue.size > 0) {
            this.queue.forEach((cb) => {
                cb();
            });

            this.queue.clear();
        }
    }

    public initializeBatching(): void {
        addEventListener('visibilitychange', () => {
            if (document.visibilityState === 'hidden') {
                this.flushQueue();
            }
        });
    }
}

Here's what I'm trying to achieve in my tests:

Testing addToQueue method: I want to ensure that calling addToQueue adds a function to the queue.

describe('addToQueue', () => {
    it('should add a function to the queue', () => {
        const mockFunction = jest.fn();
        const report = new Report();
        report.addToQueue(mockFunction);
        expect((report as any).queue.size).toBe(1); // Accessing protected property directly for testing
    });
});

However, I'm encountering this error: Property 'queue' is protected and only accessible within class 'CallbackManager' and its subclasses.

Testing initializeBatching method: I want to verify that the visibilitychange event listener is added when initializeBatching is called. Testing flushQueue method indirectly: I also want to test whether the flushQueue method is called when the visibilitychange event occurs, but flushQueue is a private method. I'd appreciate any insights on how to approach these tests effectively in TypeScript. Thank you!

Upvotes: 0

Views: 66

Answers (1)

Joe
Joe

Reputation: 186

You should be testing that your mock function was called.

expect(mockFunction).toHaveBeenCalled();

Upvotes: 0

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