The trunk as of r9570 has bit error rate testing scripts in a new
examples directory:
http://gnuradio.org/trac/browser/gnuradio/trunk/gnuradio-examples/python/digital-bert
These are a BPSK transmitter/receiver pair with SNR and BER estimation.
Please give them a spin and let me know how they work for you.
The functionality is supported by several new blocks in gnuradio-core:
gr.scrambler_bb() - LFSR based scrambler
gr.descrambler_bb() - LFSR based descrambler
gr.probe_mpsk_snr_c() - MPSK signal-to-noise ratio estimator using the
Squared Signal over Noise Variance (SNV) technique.
gr.probe_density_b() - Calculates bit density from LSBs of input stream
The BER tester works by scrambling an all 1s sequence in the modulator,
then descrambling the received sequence and measuring the density of 0s.