ossl_quic_sstream_get_buffer_size
size_t ossl_quic_sstream_get_buffer_size(QUIC_SSTREAM *qss);
size_t cur_sz = ossl_quic_sstream_get_buffer_size(sstream);
ossl_quic_sstream_get_buffer_size);
if (!TEST_size_t_eq(ossl_quic_sstream_get_buffer_size(sstream), init_size))