Use float in scipy.signal.resample. int16 renders a zero output vector.

                for i in range(nchannels):

                    tmpfile_ref = Path(tmpdir).joinpath(f"ref_ch{i+1}.wav")

                    tmpfile_test = Path(tmpdir).joinpath(f"test_ch{i+1}.wav")

                    r48 = resample(ref[:, i], fs, 48000)

                    t48 = resample(test[:, i], fs, 48000)

                    r48 = resample(ref[:, i].astype(float), fs, 48000).astype(np.dtype('int16')) # Convert to float for resample, then to int16 for wavfile.write

                    t48 = resample(test[:, i].astype(float), fs, 48000).astype(np.dtype('int16'))

                    wavfile.write(str(tmpfile_ref), 48000, r48)

                    wavfile.write(str(tmpfile_test), 48000, t48)

                    out = subprocess.check_output([mld, tmpfile_ref, tmpfile_test])