Indeed, a good thing to be tested o my side. I think we can emulate it if missing using `process.nextTick()`. Maybe something like the following:

```javascript
setImmediate = setImmediate || function(fn) {
    process.nextTick(fn, arguments.xxx());
};
```

Where `arguments.xxx()` is the necessary code to get rid of the leading arg (which is already bound to `fn`).

Opinion?