fix: stop target scrapes on a failed request

tests/test_target_scrapers.py

@@ -0,0 +1,64 @@
+"""A target scraper that cannot read its source writes nothing.
+
+The EmuDeck, RetroPie and RetroArch scrapers turned a failed request (an
+anonymous API quota, a moved buildbot directory) into an empty core list
+and wrote the file anyway: a target vanished, or kept no cores, and the
+packs built for it shrank without an error.
+"""
+
+from __future__ import annotations
+
+import sys
+import unittest
+import urllib.error
+from pathlib import Path
+from unittest import mock
+
+REPO_ROOT = Path(__file__).resolve().parent.parent
+sys.path.insert(0, str(REPO_ROOT))
+
+from scripts.scraper.targets import (  # noqa: E402
+    emudeck_targets_scraper,
+    retroarch_targets_scraper,
+    retropie_targets_scraper,
+)
+
+
+def _refuse(*_args, **_kwargs):
+    raise urllib.error.HTTPError("https://api.github.com/x", 403, "rate limited", {}, None)
+
+
+class FailedRequestsStopTheScrape(unittest.TestCase):
+    def test_every_scraper_raises(self):
+        for module in (
+            emudeck_targets_scraper,
+            retropie_targets_scraper,
+            retroarch_targets_scraper,
+        ):
+            with self.subTest(scraper=module.__name__):
+                with mock.patch.object(module.urllib.request, "urlopen", _refuse):
+                    with self.assertRaises(RuntimeError):
+                        module.Scraper().fetch_targets()
+
+    def test_an_empty_listing_is_not_a_target(self):
+        class _Empty:
+            def __enter__(self):
+                return self
+
+            def __exit__(self, *exc):
+                return False
+
+            def read(self):
+                return b"[]"
+
+        for module in (emudeck_targets_scraper, retropie_targets_scraper):
+            with self.subTest(scraper=module.__name__):
+                with mock.patch.object(
+                    module.urllib.request, "urlopen", lambda *a, **k: _Empty()
+                ):
+                    with self.assertRaises(RuntimeError):
+                        module.Scraper().fetch_targets()
+
+
+if __name__ == "__main__":
+    unittest.main()