Why does this change?

The reason is that because the asyncify continuation are now run in callUserCallback the handleException: got unexpected exception, calling quit_` which sets the node exit code to non-zero.

This test explicit has delayed_throw in it which throws and exception in an asyncify continuation.

But that delayed throw is handled early in the test,

    let delayedThrowResult = Module["delayed_throw"]();
    assert(delayedThrowResult instanceof Promise);
    let err = await delayedThrowResult.then(() => '', err => err.message);
    assert(err === 'my message', `"${err}" doesn't contain the expected error`);

The rest of the test runs after those lines, and it exits without error?

The .then(() => '', err => err.message); part handles the error, but the exit code is remembered because handleExcetpion calls quit_ which under node sets the overall process exit code:

So its kind of like the node implementation is remember the exit code even though the exception was handled further up. I don't know if this is ideal, but I imagine changing it would be very hard at this point.

I see. Yeah, probably not worth changing.

How about adding a comment in the python file, explaining why we expect the test to fail? Otherwise it is quite surprising I think.

Agreed