add unit tests to bstr* functions

bstrstart.c

@@ -4,3 +4,12 @@
 size_t bstrstart(const char* a) {
   if (*a) return 0; else return 5;
 }
+
+#ifdef UNITTEST
+#include <assert.h>
+
+int main() {
+  assert(bstrstart("foo") == 0);
+  assert(bstrstart("\x00\x03\x00\x00\x00""foo") == 5);
+}
+#endif