Preserve SpaceDevs caches on disk write failures

tests/test_spacedevs_cache.py

@@ -0,0 +1,66 @@
+"""SpaceDevs caches survive empty files and failed disk writes."""
+
+import errno
+import json
+from datetime import datetime, timedelta
+from pathlib import Path
+from unittest.mock import Mock
+
+import pytest
+
+from agenda import thespacedevs
+
+
+@pytest.mark.parametrize("contents", ["", "{", "[]", '{"detail": "throttled"}'])
+def test_launch_cache_falls_back_to_usable_file(tmp_path: Path, contents: str) -> None:
+    old = datetime.now() - timedelta(days=2)
+    (tmp_path / old.strftime("%Y-%m-%d_%H:%M:%S.json")).write_text('{"results": []}')
+    (tmp_path / datetime.now().strftime("%Y-%m-%d_%H:%M:%S.json")).write_text(contents)
+    assert thespacedevs.load_cached_launches(str(tmp_path)) == {"results": []}
+    assert thespacedevs.read_cached_launches(str(tmp_path)) == []
+    assert not thespacedevs.is_launches_cache_fresh(str(tmp_path))
+
+
+def test_empty_file_is_not_parsed(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch
+) -> None:
+    filename = tmp_path / "empty.json"
+    filename.touch()
+    parser = Mock(side_effect=AssertionError("empty file must not be parsed"))
+    monkeypatch.setattr("agenda.thespacedevs.json.load", parser)
+    assert thespacedevs.read_json_cache(str(filename)) is None
+    parser.assert_not_called()
+
+
+@pytest.mark.parametrize("existing", [False, True])
+@pytest.mark.parametrize("failure", ["fsync", "replace"])
+def test_disk_failure_preserves_cache(
+    tmp_path: Path, monkeypatch: pytest.MonkeyPatch, existing: bool, failure: str
+) -> None:
+    filename = tmp_path / "cache.json"
+    original = '{"results": ["old"]}'
+    if existing:
+        filename.write_text(original)
+    fail = Mock(side_effect=OSError(errno.ENOSPC, "No space left on device"))
+    monkeypatch.setattr(f"agenda.thespacedevs.os.{failure}", fail)
+    with pytest.raises(OSError, match="No space left"):
+        thespacedevs.write_json_cache(str(filename), {"results": ["new"]})
+    if existing:
+        assert filename.read_text() == original
+    else:
+        assert not filename.exists()
+    assert not list(tmp_path.glob(".cache-*"))
+
+
+def test_successful_write_replaces_empty_file(tmp_path: Path) -> None:
+    filename = tmp_path / "cache.json"
+    filename.touch()
+    thespacedevs.write_json_cache(str(filename), {"results": []})
+    assert json.loads(filename.read_text()) == {"results": []}
+    assert not list(tmp_path.glob(".cache-*"))
+
+
+def test_all_empty_launch_files_return_no_cache(tmp_path: Path) -> None:
+    (tmp_path / "2026-09-30_12:00:00.json").touch()
+    assert thespacedevs.load_cached_launches(str(tmp_path)) is None
+    assert not thespacedevs.is_launches_cache_fresh(str(tmp_path))