fix: lay out truth with the pack mode rule

tests/test_truth_layout.py

@@ -0,0 +1,55 @@
+"""Truth lays a core out the way verify and the pack builder do.
+
+truth.py kept its own rule: with no standalone_cores it read the profile
+type, called a dual profile "both" and a standalone one "standalone", and
+kept `mode: standalone` files that runs_standalone, and so the pack, leave
+out on RetroBat, EmuDeck and RetroDECK.
+"""
+
+from __future__ import annotations
+
+import sys
+import unittest
+from pathlib import Path
+
+REPO_ROOT = Path(__file__).resolve().parents[1]
+sys.path.insert(0, str(REPO_ROOT / "scripts"))
+
+from truth import generate_platform_truth  # noqa: E402
+
+
+def _names(truth: dict) -> set[str]:
+    return {
+        f["name"]
+        for system in truth.get("systems", {}).values()
+        for f in system.get("files", [])
+    }
+
+
+class TruthFollowsRunsStandalone(unittest.TestCase):
+    PROFILE = {
+        "emulator": "Dual",
+        "type": "standalone + libretro",
+        "systems": ["sony-playstation"],
+        "files": [
+            {"name": "both.bin", "system": "sony-playstation", "md5": "a" * 32},
+            {"name": "only_sa.bin", "system": "sony-playstation", "md5": "b" * 32,
+             "mode": "standalone"},
+            {"name": "only_lr.bin", "system": "sony-playstation", "md5": "c" * 32,
+             "mode": "libretro"},
+        ],
+    }
+
+    def test_no_standalone_cores_means_libretro_layout(self):
+        config = {"cores": ["dual"], "systems": {}}
+        truth = generate_platform_truth("p", config, {}, {"dual": self.PROFILE})
+        self.assertEqual(_names(truth), {"both.bin", "only_lr.bin"})
+
+    def test_named_standalone_core_gets_its_files(self):
+        config = {"cores": ["dual"], "standalone_cores": ["dual"], "systems": {}}
+        truth = generate_platform_truth("p", config, {}, {"dual": self.PROFILE})
+        self.assertEqual(_names(truth), {"both.bin", "only_sa.bin"})
+
+
+if __name__ == "__main__":
+    unittest.main()