test(e2e): add SHA256-verified dataset downloader + EuRoC registry entry

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/e2e/test_download.py

@@ -0,0 +1,56 @@
+"""Dataset downloader — URL registry + SHA256 verification."""
+
+import hashlib
+from pathlib import Path
+
+import pytest
+
+from gps_denied.testing.download import (
+    DATASET_REGISTRY,
+    DatasetSpec,
+    verify_sha256,
+    download_dataset,
+)
+
+
+def test_registry_has_euroc():
+    assert "euroc_mh01" in DATASET_REGISTRY
+    spec = DATASET_REGISTRY["euroc_mh01"]
+    assert isinstance(spec, DatasetSpec)
+    assert spec.url.startswith("http")
+    assert len(spec.sha256) == 64
+
+
+def test_verify_sha256_matches(tmp_path: Path):
+    data = b"hello world"
+    f = tmp_path / "x.bin"
+    f.write_bytes(data)
+    expected = hashlib.sha256(data).hexdigest()
+    assert verify_sha256(f, expected) is True
+
+
+def test_verify_sha256_mismatch(tmp_path: Path):
+    f = tmp_path / "x.bin"
+    f.write_bytes(b"hello world")
+    assert verify_sha256(f, "0" * 64) is False
+
+
+def test_download_skip_if_present(tmp_path: Path, monkeypatch):
+    f = tmp_path / "cached.zip"
+    f.write_bytes(b"cached")
+    spec = DatasetSpec(
+        url="http://example.invalid/cached.zip",
+        sha256=hashlib.sha256(b"cached").hexdigest(),
+        target_subdir="cached",
+    )
+    # Should return the path without hitting the network
+    called = {"n": 0}
+
+    def fake_get(*args, **kwargs):
+        called["n"] += 1
+        raise AssertionError("download should have been skipped")
+
+    monkeypatch.setattr("urllib.request.urlretrieve", fake_get)
+    result = download_dataset(spec, f)
+    assert result == f
+    assert called["n"] == 0