use a single-tone sine wave, fin = fs/(2*bw*osr), collect output bit stream, e.g. 1-bit: +1, +1, -1, +1, -1, ... then do fft to look at the specturm and calculate the snr
In general do a fft of the signal (remember fftshift) extract the fundamental signal power and sum the noise power. Then do Signal Power/ Noise Power. Check this MATLAB code: