class Example {
    foo(maybe: number | undefined) { }
    str(str: string) { }
    compare(ex: Example) { }
}

class Override extends Example {
    foo(maybe: number) { } // Bad: should have error.
    str(str: 'override') { } // Bad: should have error.
    compare(ex: Override) { } // Bad: should have error.
}

const ex: Example = new Override();
ex.foo(undefined);
ex.str('anything');
ex.compare(new Example());