Run library, checks and downloads in background threads with parallel fetching

tests/test_workers.py

@@ -0,0 +1,68 @@
+"""Tests for background worker threading helpers."""
+
+import os
+import time
+
+os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
+
+from PySide6.QtCore import QObject  # noqa: E402
+from PySide6.QtWidgets import QApplication  # noqa: E402
+
+from src.ui.workers import FetchWorker, run_on_thread  # noqa: E402
+
+
+def _app() -> QApplication:
+    return QApplication.instance() or QApplication([])
+
+
+def _spin_until(app: QApplication, predicate, timeout: float = 5.0) -> None:
+    deadline = time.time() + timeout
+    while not predicate() and time.time() < deadline:
+        app.processEvents()
+        time.sleep(0.01)
+
+
+def test_worker_runs_when_only_local_reference() -> None:
+    """Regression: a worker created in a local scope must still run.
+
+    run_on_thread must keep the worker alive; otherwise it is garbage-collected
+    and its `run` slot is never invoked (the 'refresh does nothing' bug).
+    """
+    app = _app()
+    owner = QObject()
+    captured: dict[str, object] = {}
+
+    def start() -> None:
+        worker = FetchWorker(lambda progress: 42)
+        worker.result.connect(lambda r: captured.update(result=r))
+        run_on_thread(owner, worker)
+        # `worker` goes out of scope here
+
+    start()
+    _spin_until(app, lambda: "result" in captured)
+    assert captured.get("result") == 42
+
+
+def test_progress_and_cleanup() -> None:
+    app = _app()
+    owner = QObject()
+    progress: list[tuple[int, int]] = []
+    captured: dict[str, object] = {}
+
+    def fn(report) -> str:
+        report(1, 2)
+        report(2, 2)
+        return "ok"
+
+    worker = FetchWorker(fn)
+    worker.progress.connect(lambda d, t: progress.append((d, t)))
+    worker.result.connect(lambda r: captured.update(result=r))
+    run_on_thread(owner, worker)
+
+    _spin_until(app, lambda: "result" in captured)
+    # let the thread.finished cleanup run
+    _spin_until(app, lambda: not owner._active_threads)
+
+    assert captured.get("result") == "ok"
+    assert (2, 2) in progress
+    assert owner._active_threads == []