it('throws a precise error when the scope document size field is negative', () => {
      // Craft a code_w_scope element whose scope objectSize = -1.
      //
      // The totalSize cross-check computes:
      //   4 (totalSize field) + 4 (string_size field) + stringSize + objectSize
      // With stringSize = 6 ("hello\0") and objectSize = -1:
      //   4 + 4 + 6 + (-1) = 13, which equals totalSize = 13.
      // Both inequality guards pass, and 13 also clears the minimum-length check (>= 13).
      //
      // Without the objectSize <= 0 guard the frame is created with lastIndex = _index - 1.
      // Since lastIndex is already behind the current index, the outer null terminator is
      // consumed by the scope's terminator check, which fails the exact-match (index !== lastIndex)
      // and throws 'Bad BSON Document: object not properly terminated' — pointing at the outer
      // document rather than the malformed scope size field.  The fix produces a precise error
      // from the right layer instead.
      const buf = bufferFromHexArray([
        '0f',                                    // BSON_DATA_CODE_W_SCOPE
        '6600',                                  // key 'f' + null
        int32LEToHex(13),                        // totalSize = 4+4+6+(-1) = 13
        int32LEToHex(6),                         // code string length = 6 ("hello" + null)
        '68656c6c6f00',                          // code string "hello\0"
        'ffffffff'                               // scope objectSize = -1 — the malicious value
      ]);
      expect(() => BSON.deserialize(buf)).to.throw(BSON.BSONError, 'bad scope document size');
    });