tests: cover the roster and the command line

The roster tests pin down the .old backup rotation and the five minute
periodic save, with a fake clock in place of datetime.

The command line tests call main() in-process with the save and data
paths in a temporary directory, so coverage counts them. They cover
listing, loading, importing and exporting saves, dumping and loading
word lists, and the first-run character creation. The curses UI is
swapped for a stub there so a stray code path fails instead of taking
over the terminal.

--load-save 0 falls through to the menu and --load-save -1 plays the
last character instead of being rejected; both are marked xfail.

A shared fixture restores pytest's SIGINT handler after the UIs
install their own.

tests/test_roster.py

@@ -0,0 +1,131 @@
+import pickle
+from datetime import datetime, timedelta
+from pathlib import Path
+
+import pytest
+from saves import hero
+
+from pqcli import roster as roster_module
+from pqcli.roster import Roster
+
+START = datetime(2024, 1, 1, 12, 0, 0)
+
+
+class Clock:
+    """Stands in for datetime in pqcli.roster; only now() is used."""
+
+    current = START
+
+    @classmethod
+    def now(cls) -> datetime:
+        return cls.current
+
+    @classmethod
+    def advance(cls, seconds: float) -> None:
+        cls.current += timedelta(seconds=seconds)
+
+
+@pytest.fixture
+def clock(monkeypatch: pytest.MonkeyPatch) -> type[Clock]:
+    monkeypatch.setattr(Clock, "current", START)
+    monkeypatch.setattr(roster_module, "datetime", Clock)
+    return Clock
+
+
+def names(path: Path) -> list[str]:
+    return [player.name for player in pickle.loads(path.read_bytes())]
+
+
+def test_load_missing_file_gives_empty_roster(tmp_path: Path) -> None:
+    path = tmp_path / "nowhere" / "save.dat"
+    roster = Roster.load(path)
+    assert roster.players == []
+    assert roster.path == path
+    assert not path.parent.exists()
+
+
+def test_load_accepts_a_string_path(tmp_path: Path) -> None:
+    path = tmp_path / "save.dat"
+    Roster(path, [hero("Ann")]).save()
+    assert Roster.load(str(path)).path == path
+
+
+def test_save_then_load_round_trip(tmp_path: Path) -> None:
+    path = tmp_path / "deep" / "dir" / "save.dat"
+    player = hero("Ann", ticks=1000)
+    Roster(path, [player, hero("Bob")]).save()
+
+    loaded = Roster.load(path).players
+    assert [p.name for p in loaded] == ["Ann", "Bob"]
+    assert loaded[0].level == player.level
+    assert loaded[0].inventory.gold == player.inventory.gold
+    assert loaded[0].quest_book.quests == player.quest_book.quests
+
+
+def test_save_keeps_the_previous_save_as_old(tmp_path: Path) -> None:
+    path = tmp_path / "save.dat"
+    old = tmp_path / "save.dat.old"
+    roster = Roster(path, [hero("Ann")])
+
+    roster.save()
+    assert names(path) == ["Ann"]
+    assert not old.exists()
+
+    roster.players.append(hero("Bob"))
+    roster.save()
+    assert names(path) == ["Ann", "Bob"]
+    assert names(old) == ["Ann"]
+
+    roster.players.pop(0)
+    roster.save()
+    assert names(path) == ["Bob"]
+    assert names(old) == ["Ann", "Bob"]
+
+    assert sorted(p.name for p in tmp_path.iterdir()) == [
+        "save.dat",
+        "save.dat.old",
+    ]
+
+
+def test_save_periodically_waits_five_minutes(
+    tmp_path: Path, clock: type[Clock]
+) -> None:
+    path = tmp_path / "save.dat"
+    roster = Roster(path, [hero("Ann")])
+
+    clock.advance(299)
+    roster.save_periodically()
+    assert not path.exists()
+
+    clock.advance(1)
+    roster.save_periodically()
+    assert names(path) == ["Ann"]
+
+    # the timer starts over after a save
+    roster.players.append(hero("Bob"))
+    clock.advance(299)
+    roster.save_periodically()
+    assert names(path) == ["Ann"]
+
+    clock.advance(1)
+    roster.save_periodically()
+    assert names(path) == ["Ann", "Bob"]
+
+
+def test_manual_save_restarts_the_periodic_timer(
+    tmp_path: Path, clock: type[Clock]
+) -> None:
+    path = tmp_path / "save.dat"
+    roster = Roster(path, [hero("Ann")])
+
+    clock.advance(200)
+    roster.save()
+    roster.players.append(hero("Bob"))
+
+    clock.advance(200)
+    roster.save_periodically()
+    assert names(path) == ["Ann"]
+
+    clock.advance(100)
+    roster.save_periodically()
+    assert names(path) == ["Ann", "Bob"]