tsmockito - How to mock a function that takes a lambda argument

Question

I have a function that takes a lambda (and the lambda also takes an argument). How can I mock the function?

In the example below, I'm trying to mock connection.xmppStanzas:

Example class:

type Matcher<T> = (t: T) => boolean;

const myMatcher: Matcher<Element> = (id: string) => ...;

class SomeClass {
    constructor(private readonly idSource: IdSource,
                private readonly connection: XmppConnection) {}

    doSomething() {
        const id = this.idSource.getId();
        this.connection.xmppStanzas(myMatcher(id)).pipe(
            ...do something with the stanza
        );
    }

}

Test for SomeClass:

describe('SomeClass', () => {
    let idSource: IdSource;
    let connection: XmppConnection;
    let instance: SomeClass;

    beforeEach(() => {
        idSource = mock(idSource);
        connection = mock(XmppConnection);

        instance = new SomeClass(
            instance(idSource),
            instance(connection)
        );

        when(idSource.getId()).thenReturn(someId);
    });

    it('this is an example test', () => {
        const stanzas$ = new BehaviorSubject(myTestStanza);
        when(connection.xmppStanzas(myMatcher(someId))).thenReturn(stanzas$);

        ...test that the right thing was done with the stanza

        verify(connection.xmppStanzas(myMatcher(someId))).once()
    });
});

The problem is the when doesn't return the stanzas stream (so all my tests to make sure something was done with the stanza fail) and the verify I threw in at the end real quick also fails, proving why the when isn't returning the right value: because tsmockito can't match the lambda. Apparently when you pass an argument to the lambda, it makes a new instance and even deepEqual won't work on it.

I could do when(connection.xmppStanzas(anything())).thenReturn(stanzas$) but I really want to make sure that my function doSomething() is retrieving the ID correctly and passing it to my matcher. That's part of the test.

So my question is: how do I deal with mocking a function that takes a lambda that takes an argument??