Chore: Add a guard test so duplicate sample files cannot come back

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

src/documents/tests/test_sample_files.py

@@ -1,6 +1,8 @@
 import hashlib
+from collections import defaultdict
 from pathlib import Path
 
+from paperless_testing.samples import SHARED_SAMPLES_DIR
 from paperless_testing.samples import SIMPLE_DIGITAL_PDF
 from paperless_testing.samples import install_document_samples
 
@@ -32,3 +34,26 @@ def test_install_recreates_every_historical_opaque_name(tmp_path: Path) -> None:
 def test_install_uses_the_shared_bytes(tmp_path: Path) -> None:
     install_document_samples(tmp_path)
     assert _sha(tmp_path / "originals" / "0000001.pdf") == _sha(SIMPLE_DIGITAL_PDF)
+
+
+APP_SAMPLE_TREES = [
+    Path(__file__).parent / "samples",
+    Path(__file__).parents[2] / "paperless" / "tests" / "samples",
+    Path(__file__).parent / "examples",
+    SHARED_SAMPLES_DIR,
+]
+
+
+def test_no_two_sample_files_have_identical_bytes() -> None:
+    by_hash: dict[str, list[Path]] = defaultdict(list)
+    for tree in APP_SAMPLE_TREES:
+        for path in tree.rglob("*"):
+            if path.is_file():
+                by_hash[_sha(path)].append(path)
+    duplicates = {h: ps for h, ps in by_hash.items() if len(ps) > 1}
+    lines = ["  " + ", ".join(str(p) for p in ps) for ps in duplicates.values()]
+    message = (
+        "Duplicate sample files, move one to paperless_testing/sample_files:\n"
+        + "\n".join(lines)
+    )
+    assert not duplicates, message