How to detect subscription leakage by tracking their total number?

[ArtemAvramenko]

Meaning not an individual Observable, but all subscriptions in all currently existing Observables.

This is necessary so that testers can detect bugs with a constantly growing number of subscriptions.
It is important to catch the very fact of subscription leakage, further detailed research will be done by developers.

Now such bugs are detected very slowly by indirect signs, such as obvious memory leaks. I would like testers to be able to see the number of active subscriptions as an indicator of the application's health.

[ArtemAvramenko]

This is the solution I've come up with so far:

import { Subscriber } from 'rxjs';

Object.defineProperty(Subscriber.prototype, 'closed', {
    get: function (this: { __closed: boolean; }) { return this.__closed; },
    set: function (this: { __closed: boolean; }, value: boolean) {
        this.__closed = value;
        totalSubscriptionCounter += value ? -1 : 1;
    }
});

If anyone knows any other scenarios of subscription leaks, please tell me.