Allow to reset the value of MockFunctionContext.#calls

[GauBen]

What is the problem this feature will solve?

I use globally mocked objects in my tests to allow them to run without an environment:

// Something that looks like a nodemailer object
export const mailer = {
  sendMail: mock.fn(() => Promise.resolve())
};

Because it's global, tests can pollute each other:

it('works', () => {
  mailer.sendMail({ to: "user@example.com" });
  assert.equal(mailer.sendMail.mock.callCount(), 1);
});

it('also works', () => {
  mailer.sendMail({ to: "user@example.com" });
  assert.equal(mailer.sendMail.mock.callCount(), 1); // It fails here, `callCount()` is now 2
});

What is the feature you are proposing to solve the problem?

I want to be able to reset mailer.sendMail.mock.calls:

describe('something', () => {
  beforeEach(() => {
    mailer.sendMail.mock.reset(); // Method name open to bikeshedding
  })
})

node/lib/internal/test_runner/mock.js

Lines 46 to 52 in 8a4d7ac

	get calls() {
	return ArrayPrototypeSlice(this.#calls, 0);
	}
	callCount() {
	return this.#calls.length;
	}

It could be as simple as:

reset() {
  this.#calls = [];
}

If you're okay with this design, I'm interested in creating a PR with the feature and associated tests.

What alternatives have you considered?

Use another mocking library

Current workaround

I resorted to this hack:

let prevCount = 0;
mailer.sendMail.mock.constructor.prototype.lastCalls = function () {
  const count = this.callCount();
  const tail = this.calls.slice(prevCount);
  prevCount = count;
  return tail;
};

[GauBen]

Addressed by #45710