Harden tests flagged in code review

Strengthen weak-assertion / false-confidence tests:

  - test_alfcrypto: replace the tautological ctx_init determinism check
    with an independent golden vector, and add a golden Topaz decrypt
    vector that does not rely on the test's own inverse helper (so a
    systematic cipher bug is caught, not just round-trip symmetry). Pin
    the PC1 bad-key assertion to match="Bad key length", and load
    alfcrypto via the dedrm package so the test exercises the same module
    object that topazextract/mobidedrm import.
  - test_mobidedrm: pin the PC1 bad-key assertion to the guard message.
  - test_topazextract: make the path-traversal regression rely on the
    depth-independent positive oracle (the sanitised file must land inside
    outdir, which fails against the pre-fix code) plus an exact-contents
    check, instead of brittle parent-path negatives.
  - test_erdr2pml: narrow the import skip to only the missing-cgi case so
    a genuinely broken module fails loudly instead of silently skipping.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_alfcrypto.py

@@ -6,7 +6,10 @@ import pytest
 
 import dedrm_test_utils as U
 
-alf = U.load("alfcrypto")
+# Load via the `dedrm` package so we exercise the same module object that
+# topazextract/mobidedrm import through `from .alfcrypto import ...`, rather
+# than a second top-level copy.
+alf = U.load("alfcrypto", package="dedrm")
 
 
 def test_pc1_roundtrip():
@@ -18,7 +21,8 @@ def test_pc1_roundtrip():
 
 
 def test_pc1_rejects_bad_key_length():
-    with pytest.raises(Exception):
+    # Pin the specific guard, not just "some exception".
+    with pytest.raises(Exception, match="Bad key length"):
         alf.Pukall_Cipher().PC1(b"\x00" * 8, b"data............", decryption=False)
 
 
@@ -42,8 +46,21 @@ def test_topaz_cipher_roundtrip():
     assert recovered == plaintext
 
 
-def test_topaz_ctx_init_is_deterministic():
-    assert alf.Topaz_Cipher().ctx_init(b"abc") == alf.Topaz_Cipher().ctx_init(b"abc")
+def test_topaz_ctx_init_golden():
+    # Independent golden vector pins the key-schedule math; a bare determinism
+    # check (ctx_init(x) == ctx_init(x)) would pass for any implementation.
+    assert alf.Topaz_Cipher().ctx_init(b"abc") == [426181496, 3966955212]
+
+
+def test_topaz_decrypt_golden():
+    # Golden oracle independent of the test's own inverse helper: a fixed
+    # ciphertext + key must always decrypt to exactly these bytes. This catches
+    # a systematic state-update bug that the round-trip test cannot.
+    ctx = alf.Topaz_Cipher().ctx_init(b"topaz-key")
+    out = alf.Topaz_Cipher().decrypt(bytes(range(32)), list(ctx)).encode("latin-1")
+    assert out == bytes.fromhex(
+        "e64653fbb4c4ad06981b51a0e53cd17ad9c7bc72932626ed35b935791f4fd769"
+    )
 
 
 def test_pbkdf2_matches_hashlib():

tests/test_erdr2pml.py

@@ -13,9 +13,15 @@ import dedrm_test_utils as U
 try:
     erdr2pml = U.load("erdr2pml", package="dedrm")
     _skip_reason = None
-except Exception as exc:  # pragma: no cover - depends on interpreter / deps
-    erdr2pml = None
-    _skip_reason = "erdr2pml not importable: {0}".format(exc)
+except ImportError as exc:  # pragma: no cover - depends on interpreter / deps
+    # Only tolerate the specific "no cgi backport" case (Python 3.13+ without
+    # legacy-cgi). Any other import error means the module is genuinely broken
+    # and must fail loudly rather than silently skip.
+    if getattr(exc, "name", None) == "cgi":
+        erdr2pml = None
+        _skip_reason = "erdr2pml needs the 'cgi' module (install legacy-cgi on Python 3.13+)"
+    else:
+        raise
 
 pytestmark = pytest.mark.skipif(erdr2pml is None, reason=_skip_reason or "")
 

tests/test_mobidedrm.py

@@ -16,7 +16,7 @@ def test_pc1_roundtrip():
 
 
 def test_pc1_rejects_bad_key_length():
-    with pytest.raises(Exception):
+    with pytest.raises(Exception, match="Bad key length"):
         md.PC1(b"\x00" * 8, b"data............", decryption=False)
 
 

tests/test_topazextract.py

@@ -41,11 +41,16 @@ def test_extractfiles_strips_path_traversal(tmp_path):
 
     book.extractFiles()
 
-    # The traversal sequence was stripped: nothing was written above outdir.
+    # Primary oracle (independent of traversal depth): with the fix, basename()
+    # strips every "../" so the record always lands INSIDE outdir. The pre-fix
+    # code did os.path.join(outdir, "../../evil0000.dat"), writing OUTSIDE outdir,
+    # so this assertion fails without the fix no matter how deep tmp_path nests.
+    assert (outdir / "evil0000.dat").read_bytes() == b"PWNED"
+    # outdir contains exactly that one sanitised file, nothing unexpected.
+    assert sorted(p.name for p in outdir.iterdir()) == ["evil0000.dat"]
+    # Defense in depth: nothing escaped to the dirs the "../../" payload targets.
     assert not (tmp_path / "evil0000.dat").exists()
     assert not (tmp_path.parent / "evil0000.dat").exists()
-    # The (sanitised) write landed safely inside outdir.
-    assert (outdir / "evil0000.dat").read_bytes() == b"PWNED"
 
 
 def test_extractfiles_writes_normal_record(tmp_path):