module renaming by declaration

[Christof Schardt via Digitalmars-d-learn]

The module declaration allows to define a module name different from the 
filename.
(TDPL sec. 11.1.8)
I tried a simple example:

File test.d:
---------
 import bbb;
---------
File aaa.d (same directory):
---------
  module bbb;
---------

Running
 rdmd test.d
does give an error: "module bbb is in file bbb.d which cannot be read"

What am I doing wrong?