It would be better if this was a loop, and included in the test file itself.  Fixtures just make tests harder to read.

That is, in the test-child-process-stdout-flush-exit.js, it could do something like:

```javascript
if (process.argv[2] === 'child') {
  console.log('hello');
  for (var i = 0; i < 256; i++)
    console.log('filler');
  console.log('goodbye');
  return;
}
```

And then `spawn(process.argv, [__filename, 'child'])` to run the child process.