It is tempting to do something like this:

var error = new Error('some error');

stream
  .pipe(through(function(chunk) {
    throw error ;
  }))
  .on('error', function(err) {
    assert.equal(error, err);
  });

For me because in promise throwing an exception equals rejection.

The docs should tell what really happens when exceptions are thrown in these kind of functions (_read, _write, _writev, _transform, _flush).