diff --git a/buffer/bs_capacityassert.c b/buffer/bs_capacityassert.c
index fbb0568..1e2ca93 100644
--- a/buffer/bs_capacityassert.c
+++ b/buffer/bs_capacityassert.c
@@ -11,3 +11,31 @@ int bs_capacityassert(struct bytestream* bs,size_t capacity) {
   }
   return 1;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+#undef UNITTEST
+#include "buffer/bs_err.c"
+
+int main() {
+  struct bytestream bs;
+  // test basic functionality
+  bs.cur=0; bs.max=100;
+  assert(bs_capacityassert(&bs, 100) == 1);
+  assert(bs_err(&bs) == 0);
+
+  bs.cur=50; bs.max=100;
+  assert(bs_capacityassert(&bs, 50) == 1);
+  assert(bs_err(&bs) == 0);
+
+  assert(bs_capacityassert(&bs, 51) == 0);
+  assert(bs_err(&bs));
+
+  // try to provoke a numeric overflow
+  bs.cur=100; bs.max=(size_t)-1;
+  assert(bs_capacityassert(&bs, (size_t)-50) == 0);
+  assert(bs_err(&bs));
+}
+
+#endif
diff --git a/buffer/bs_get.c b/buffer/bs_get.c
index 1b9eb9a..ef29e98 100644
--- a/buffer/bs_get.c
+++ b/buffer/bs_get.c
@@ -38,13 +38,18 @@ unsigned char bs_get(struct bytestream* bs) {
   return r;
 }
 
-int bs_err(struct bytestream* bs) {
-  return (bs->cur > bs->max);
-}
-
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_err.c"
+#include "buffer/buffer_init_staticcontents.c"
+#include "buffer/bs_init_iobuf.c"
+#include "buffer/bs_init_iobuf_size.c"
+#include "buffer/buffer_getc.c"
+#include "buffer/buffer_feed.c"
+#include "buffer/buffer_stubborn2.c"
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("fnord\nx", 6);
   int i;
diff --git a/buffer/bs_init_bstream_size.c b/buffer/bs_init_bstream_size.c
index 7033360..cf9fa8e 100644
--- a/buffer/bs_init_bstream_size.c
+++ b/buffer/bs_init_bstream_size.c
@@ -19,6 +19,7 @@ void bs_init_bstream_size(struct bytestream* bs,struct bytestream* other,size_t
 
 #undef UNITTEST
 #include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
 #include "buffer/bs_capacityassert.c"
 #include "buffer/bs_init_membuf.c"
 
diff --git a/buffer/bs_init_membuf.c b/buffer/bs_init_membuf.c
index e45b251..fd1566f 100644
--- a/buffer/bs_init_membuf.c
+++ b/buffer/bs_init_membuf.c
@@ -9,6 +9,13 @@ void bs_init_membuf(struct bytestream* bs,const unsigned char* membuf,size_t len
 
 #ifdef UNITTEST
 #include <assert.h>
+
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+ssize_t buffer_getc(buffer* b,char* c) { return -1; }
+
 int main() {
   static struct bytestream bs;
   bs_init_membuf(&bs, "fnord\n", 6);
diff --git a/buffer/bs_peek.c b/buffer/bs_peek.c
index a0c784b..3fc633a 100644
--- a/buffer/bs_peek.c
+++ b/buffer/bs_peek.c
@@ -40,6 +40,17 @@ unsigned char bs_peek(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_err.c"
+#include "buffer/bs_get.c"
+#include "buffer/buffer_init_staticcontents.c"
+#include "buffer/bs_init_iobuf.c"
+#include "buffer/bs_init_iobuf_size.c"
+#include "buffer/buffer_peekc.c"
+#include "buffer/buffer_getc.c"
+#include "buffer/buffer_feed.c"
+#include "buffer/buffer_stubborn2.c"
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("fx", 1);
 
diff --git a/buffer/buffer_init_staticcontents.c b/buffer/buffer_init_staticcontents.c
index deee53e..063871e 100644
--- a/buffer/buffer_init_staticcontents.c
+++ b/buffer/buffer_init_staticcontents.c
@@ -16,6 +16,15 @@ void buffer_init_staticcontents(buffer* b, char* y, size_t len) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "byte/byte_copy.c"
+#include "buffer/buffer_get.c"
+#include "buffer/buffer_put.c"
+#include "buffer/buffer_stubborn.c"
+#include "buffer/buffer_stubborn2.c"
+#include "buffer/buffer_flush.c"
+#include "buffer/buffer_feed.c"
+
 int main() {
   buffer b;
   buffer_init_staticcontents(&b, "fnord", 5);
diff --git a/buffer/buffer_put.c b/buffer/buffer_put.c
index 9ee9a0d..2082da5 100644
--- a/buffer/buffer_put.c
+++ b/buffer/buffer_put.c
@@ -5,7 +5,7 @@
 #endif
 #include "buffer.h"
 
-extern int buffer_stubborn(ssize_t (*op)(),int fd,const char* buf, size_t len,void* cookie);
+extern ssize_t buffer_stubborn(ssize_t (*op)(),int fd,const char* buf, size_t len,void* cookie);
 
 #ifndef __unlikely
 #ifdef __GNUC__
diff --git a/buffer/buffer_stubborn.c b/buffer/buffer_stubborn.c
index 2e00418..8008878 100644
--- a/buffer/buffer_stubborn.c
+++ b/buffer/buffer_stubborn.c
@@ -1,7 +1,7 @@
 #include <errno.h>
 #include "buffer.h"
 
-int buffer_stubborn(ssize_t (*op)(),int fd,const char* buf, size_t len,void* cookie) {
+ssize_t buffer_stubborn(ssize_t (*op)(),int fd,const char* buf, size_t len,void* cookie) {
   ssize_t w;
   errno=0;
   while (len) {
diff --git a/buffer/prs_asciiz.c b/buffer/prs_asciiz.c
index 9dce998..687c55b 100644
--- a/buffer/prs_asciiz.c
+++ b/buffer/prs_asciiz.c
@@ -45,6 +45,7 @@ ssize_t prs_asciiz(struct bytestream* bs, char* dest, size_t len) {
 #undef UNITTEST
 #include "buffer/bs_init_membuf.c"
 #include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
 #include "buffer/bs_peek.c"
 
 // we use membuf here, mock buffer stuff away
diff --git a/buffer/prs_asciiz_fixedlen.c b/buffer/prs_asciiz_fixedlen.c
index cf69472..256f857 100644
--- a/buffer/prs_asciiz_fixedlen.c
+++ b/buffer/prs_asciiz_fixedlen.c
@@ -36,6 +36,7 @@ ssize_t prs_asciiz_fixedlen(struct bytestream* bs, char* dest, size_t len) {
 #undef UNITTEST
 #include "buffer/bs_init_membuf.c"
 #include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
 #include "buffer/bs_peek.c"
 
 // we use membuf here, mock buffer stuff away
diff --git a/buffer/prs_readblob.c b/buffer/prs_readblob.c
index 4da4ba6..99d60e9 100644
--- a/buffer/prs_readblob.c
+++ b/buffer/prs_readblob.c
@@ -36,3 +36,48 @@ ssize_t prs_readblob(struct bytestream* bs,unsigned char* dest,size_t destlen) {
 
     return r;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+#include "buffer/bs_capacityassert.c"
+#include "buffer/bs_init_iobuf_size.c"
+#include "buffer/bs_init_membuf.c"
+
+#include "buffer/buffer_get.c"
+#include "buffer/buffer_getc.c"
+#include "buffer/buffer_feed.c"
+#include "buffer/buffer_stubborn2.c"
+#include "byte/byte_copy.c"
+#include "open/open_read.c"
+
+int main() {
+  struct bytestream bs = BS_FROM_MEMBUF("\x34\x12", 2);
+  char buf[42];
+  assert(prs_readblob(&bs, buf, 2) == 2);
+  assert(bs_err(&bs) == 0);
+  assert(!memcmp(buf,"\x34\x12",2));
+
+  assert(prs_readblob(&bs, buf, 1) == -1);
+  assert(bs_err(&bs));
+
+  // now try to provoke integer overflow
+  bs_init_membuf(&bs, "\x34\x12", 2);
+  assert(bs_get(&bs) == 0x34);
+  assert(prs_readblob(&bs, buf, (size_t)-1) == -1);
+  // a bad implementation would add 0xffffffff to the 1 we already read and wrap to 0
+  // our code makes sure not to wrap and also limits the length of the
+  // blob to max_ssize_t (0x7fffffff).
+  assert(bs_err(&bs));
+
+  int fd = open_read("Makefile");
+  assert(fd!=-1);
+  buffer b = BUFFER_INIT(read, fd, buf+32, 10);
+  bs_init_iobuf_size(&bs, &b, 100);
+  assert(prs_readblob(&bs, buf, 20) == 20);	// make sure we can read a 20 byte blob at once even if the iobuf buffer size is smaller
+  // strace will show two read calls here
+}
+#endif
diff --git a/buffer/prs_u16.c b/buffer/prs_u16.c
index 547db1d..4e17e9d 100644
--- a/buffer/prs_u16.c
+++ b/buffer/prs_u16.c
@@ -7,6 +7,13 @@ uint16_t prs_u16(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+// mock this
+ssize_t buffer_getc(buffer* b,char* c) { return 0; }
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("\x34\x12",2);
   assert(prs_u16(&bs) == 0x1234);
diff --git a/buffer/prs_u16_big.c b/buffer/prs_u16_big.c
index 45bce8e..e02ead2 100644
--- a/buffer/prs_u16_big.c
+++ b/buffer/prs_u16_big.c
@@ -7,6 +7,13 @@ uint16_t prs_u16_big(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+// mock this
+ssize_t buffer_getc(buffer* b,char* c) { return 0; }
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("\x12\x34",2);
   assert(prs_u16_big(&bs) == 0x1234);
diff --git a/buffer/prs_u32.c b/buffer/prs_u32.c
index 354693c..555bb14 100644
--- a/buffer/prs_u32.c
+++ b/buffer/prs_u32.c
@@ -7,6 +7,13 @@ uint32_t prs_u32(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+// mock this
+ssize_t buffer_getc(buffer* b,char* c) { return 0; }
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("\x78\x56\x34\x12",4);
   assert(prs_u32(&bs) == 0x12345678);
diff --git a/buffer/prs_u32_big.c b/buffer/prs_u32_big.c
index 2aad0b3..900071e 100644
--- a/buffer/prs_u32_big.c
+++ b/buffer/prs_u32_big.c
@@ -7,6 +7,13 @@ uint32_t prs_u32_big(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+// mock this
+ssize_t buffer_getc(buffer* b,char* c) { return 0; }
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("\x12\x34\x56\x78",4);
   assert(prs_u32_big(&bs) == 0x12345678);
diff --git a/buffer/prs_u64.c b/buffer/prs_u64.c
index e139004..1103a25 100644
--- a/buffer/prs_u64.c
+++ b/buffer/prs_u64.c
@@ -11,6 +11,13 @@ uint64_t prs_u64(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+// mock this
+ssize_t buffer_getc(buffer* b,char* c) { return 0; }
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("\x78\x56\x34\x12\xef\xbe\xad\xde",8);
   assert(prs_u64(&bs) == 0xdeadbeef12345678);
diff --git a/buffer/prs_u64_big.c b/buffer/prs_u64_big.c
index 4b9edda..9d8ec9d 100644
--- a/buffer/prs_u64_big.c
+++ b/buffer/prs_u64_big.c
@@ -11,6 +11,13 @@ uint64_t prs_u64_big(struct bytestream* bs) {
 #ifdef UNITTEST
 #include <assert.h>
 
+#undef UNITTEST
+#include "buffer/bs_get.c"
+#include "buffer/bs_err.c"
+
+// mock this
+ssize_t buffer_getc(buffer* b,char* c) { return 0; }
+
 int main() {
   struct bytestream bs = BS_FROM_MEMBUF("\xde\xad\xbe\xef\x12\x34\x56\x78",8);
   assert(prs_u64_big(&bs) == 0xdeadbeef12345678);
diff --git a/parse.h b/parse.h
index 3fec6fe..cc94446 100644
--- a/parse.h
+++ b/parse.h
@@ -84,6 +84,7 @@ unsigned char bs_peek(struct bytestream* bs);
 int bs_err(struct bytestream* bs);
 
 /* Can we read this much more bytes from the bytestream? */
+/* returns 1 for yes, 0 for no */
 int bs_capacitycheck(struct bytestream* bs,size_t capacity);
 /* Like bs_capacitycheck but will set stream to error state on fail */
 int bs_capacityassert(struct bytestream* bs,size_t capacity);