Example for asserting `HttpsError` thrown by cloud function

[nilsreichardt]

It would be really nice to have an example how to assert HttpsError, which are thrown by a cloud function.

exports.testCallable = functions.https.onCall((data, context) => {
    console.log('testCallable');
    return new functions.https.HttpsError('ok', 'this is an error');
})

How to write a test, that a HttpsError with the message this is an error was thrown?