tests: cover the basic UI

Drive the line-based UI in-process: input() answers come from a list
and the output is captured. The tests walk the main menu through
creating, playing, querying, deleting, importing and exporting
characters, plus bad menu input and the Ctrl+C handler.

The play loop runs on a fake clock that advances a minute per call and
stops when time.sleep has been called a set number of times, so it
levels up and saves on schedule without waiting.

The test helpers move to tests/helpers.py, which now also holds the
input() feeder.

tests/helpers.py

@@ -0,0 +1,63 @@
+"""Characters, saves and prompts shared by the UI and CLI tests."""
+
+from collections.abc import Iterable
+from pathlib import Path
+
+import pytest
+from test_pqw import played
+
+from pqcli import pqw
+from pqcli.game_data import load_game_data
+from pqcli.mechanic import Player
+from pqcli.roster import Roster
+
+DATA = load_game_data()
+
+
+def hero(name: str = "Exportée", ticks: int = 300) -> Player:
+    """A character that has played for a while."""
+    player = played(ticks).player
+    player.name = name
+    return player
+
+
+def save_path(config: Path) -> Path:
+    """Where pqcli keeps its roster with XDG_CONFIG_HOME set to config."""
+    return config / "pqcli" / "save.dat"
+
+
+def write_roster(config: Path, *players: Player) -> Path:
+    path = save_path(config)
+    Roster(path, list(players)).save()
+    return path
+
+
+def read_names(config: Path) -> list[str]:
+    return [player.name for player in Roster.load(save_path(config)).players]
+
+
+def write_pqw(path: Path, player: Player, *, online: bool = False) -> Path:
+    """Write player as a .pqw; online adds fields the import warns about."""
+    game = pqw.export_game(player, DATA)
+    if online:
+        game["online"] = {"realm": "Alpaquil", "passkey": 1}
+    path.write_text(pqw.encode(game), encoding="ascii")
+    return path
+
+
+def feed(monkeypatch: pytest.MonkeyPatch, answers: Iterable[str]) -> None:
+    """Answer input() prompts in order; running out is a test failure.
+
+    Prompts are echoed so captured output reads like a session.
+    """
+    it = iter(answers)
+
+    def fake_input(prompt: str = "") -> str:
+        try:
+            answer = next(it)
+        except StopIteration:
+            raise AssertionError(f"unexpected prompt {prompt!r}") from None
+        print(f"{prompt}{answer}")
+        return answer
+
+    monkeypatch.setattr("builtins.input", fake_input)