Thanks for the contribution, and for thinking about boundary/cursor/stat coverage — that kind of testing is welcome.

Unfortunately I can't merge this as-is: it won't compile. test/c/test_db185.c exercises the DB 1.85 compatibility API (it #includes db_185.h and dbp is the 1.85 DB). That handle is defined in src/dbinc/db_185.in and has only these methods:

typedef struct __db {
    DBTYPE type;
    int (*close)(struct __db *);
    int (*del)(const struct __db *, const DBT *, u_int);
    int (*get)(const struct __db *, const DBT *, DBT *, u_int);
    int (*put)(const struct __db *, DBT *, const DBT *, u_int);
    int (*seq)(const struct __db *, DBT *, DBT *, u_int);
    int (*sync)(const struct __db *, u_int);
    void *internal;
    int (*fd)(const struct __db *);
} DB;

So the new code can't build here:

• dbp->cursor(...) and dbp->stat(...) — no such members on the 1.85 DB.
• cursor->c_get/c_put/c_close (DBC), and constants DB_NEXT, DB_SET, DB_KEYFIRST, DB_NOTFOUND, DB_BTREE_STAT/DB_HASH_STAT/DB_RECNO_STAT — these are the modern API, not in db_185.h (the 1.85 API iterates with seq() + R_NEXT/R_FIRST and has no cursors or stat).

A couple of other issues to flag regardless:

• char large_key[1024*1024] is a 1 MB stack array (stack overflow risk).
• In test_db_cursor, sprintf((char *)key.data, ...) writes into the buffer returned by c_get, which is owned by Berkeley DB — that's a write into library-owned memory.

Two good ways forward:

1. Best: add these cursor/stat/boundary tests against the modern API — e.g. a new test/c/ program (or extend one that uses db.h/DB_ENV), where DB->cursor, DBC->get, and DB->stat exist. That's where this coverage belongs.
2. If you specifically want to extend the 1.85 path, use only get/put/del/seq/sync with the R_* flags, and keep buffers caller-owned.

Happy to review a revised version. Closing for changes, not merging.

Thanks for the contribution — the intent (boundary conditions, cursor traversal, and stat coverage) is welcome. Unfortunately these additions can't land as written, because test/c/test_db185.c exercises the DB 1.85 compatibility API (dbopen() → struct __db), and the new code calls modern DB 4.x/5.x methods that do not exist on the 1.85 handle. From src/dbinc/db_185.in the 1.85 struct __db has exactly: close, del, get, put, seq, sync, fd — no cursor, no stat.

Blocking issues:

1. dbp->cursor(...) / cursor->c_get/c_put/c_close (won't compile). The 1.85 API has no cursor object; sequential traversal is dbp->seq(dbp, &key, &data, R_FIRST|R_NEXT). DBC and its c_* methods are the modern API and aren't declared in db_185.h.
2. dbp->stat(...) + DB_BTREE_STAT/DB_HASH_STAT/DB_RECNO_STAT (won't compile). The 1.85 handle has no stat method, and those stat structs belong to the modern API.
3. __os_free(NULL, statp) — an internal engine symbol; a test in test/c/ must not call __os_*. (Moot once #2 is dropped.)
4. 1 MB stack array (char large_key[1024*1024]) — this repo's C-test convention forbids large stack arrays (stack overflow risk); use the heap.
5. sprintf((char *)key.data, ...) after a get/c_get writes into DB-owned memory returned by the previous call — never write into memory Berkeley DB owns; and key.data may be NULL there.
6. char small_key[1] = "" can't hold the terminating NUL; and DB error codes are returned directly (don't strerror(errno) on them).

Suggested path: retarget this coverage at the modern API — the existing test/tcl suite (e.g. test001 for put/get/boundary, cursor tests, statprint001 for stat) already covers most of it, or add a C driver under test/c/ that opens a real DB_ENV/DB handle. If you specifically want 1.85-compat coverage, use seq() (there's no cursor/stat in 1.85). Happy to point at the right harness. Closing for now since it can't compile against the 1.85 header; please reopen a retargeted version.