Mocha 7: A global uncaughtException handle is leaked for every completed test runner

[weswigham]

Description

A global uncaughtException handle is leaked for every completed test runner, in turn causing a MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 uncaughtException listeners added to [process]. Use emitter.setMaxListeners() to increase limit warning to be thrown by node.

Since every handler attached is identical in content here, attaching one for the first completed runner should be just as correct (although, functionality-wise, it may need to be detcahced once a new runner has started - it's unclear how the sequencing between multiple runners is intended to work out for this handler).

Steps to Reproduce

const mocha = require("mocha");
for (let i = 0; i < 15; i++) {
    const r = new mocha.Runner(new mocha.Suite(""+i, undefined));
    r.run();
}

Expected behavior:
No warnings from node.

Actual behavior:

A MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 uncaughtException listeners added to [process]. Use emitter.setMaxListeners() to increase limit warning is printed.

Reproduces how often:
Every time. You can paste that example code into a repl.

[juergba]

@weswigham thanks for reporting and testing!