Hi Sungjin, 

Network programs benefit from TDD as much as any other program.
"MaArmoredCode" is an extension to the SUnit testing that assists with
automating the testing of network programs by conducting the test
through remote-perform calls to other Squeak images, instructing them
to exercise their own network code.  You can even simulate server or
network failures to exercise your error-handling, and then resume the
network test.

You have to define the network players and choose your own ports and
the test-play ports up front.  But once your TestCase subclass is set
up, the suite of multiple images is all launched with one-click,
courtesy of OSProcess.

  http://minnow.cc.gatech.edu/squeak/2659