Harden runtime distribution acceptance

tests/test_runtime_image_smoke.py

@@ -0,0 +1,57 @@
+from __future__ import annotations
+
+import importlib.util
+import json
+from pathlib import Path
+import sys
+import tempfile
+import unittest
+
+
+ROOT = Path(__file__).resolve().parents[1]
+SCRIPT = ROOT / "tools/checks/runtime-image-smoke.py"
+SPEC = importlib.util.spec_from_file_location("runtime_image_smoke", SCRIPT)
+assert SPEC is not None and SPEC.loader is not None
+MODULE = importlib.util.module_from_spec(SPEC)
+sys.modules[SPEC.name] = MODULE
+SPEC.loader.exec_module(MODULE)
+
+
+class RuntimeImageSmokeTests(unittest.TestCase):
+    def test_selects_the_exact_platform_digest(self) -> None:
+        with tempfile.TemporaryDirectory(prefix="govoplan-runtime-smoke-") as value:
+            path = Path(value) / "metadata.json"
+            path.write_text(
+                json.dumps(
+                    {
+                        "index": "registry.example/api@sha256:" + "a" * 64,
+                        "platforms": {
+                            "linux/amd64": "registry.example/api@sha256:" + "1" * 64,
+                            "linux/arm64": "registry.example/api@sha256:" + "2" * 64,
+                        },
+                    }
+                ),
+                encoding="utf-8",
+            )
+
+            self.assertEqual(
+                "registry.example/api@sha256:" + "2" * 64,
+                MODULE.platform_image(path, "linux/arm64", "API"),
+            )
+
+    def test_rejects_mutable_or_missing_platform_images(self) -> None:
+        with tempfile.TemporaryDirectory(prefix="govoplan-runtime-smoke-") as value:
+            path = Path(value) / "metadata.json"
+            path.write_text(
+                json.dumps({"platforms": {"linux/amd64": "registry.example/api:latest"}}),
+                encoding="utf-8",
+            )
+
+            with self.assertRaisesRegex(MODULE.SmokeError, "exact sha256"):
+                MODULE.platform_image(path, "linux/amd64", "API")
+            with self.assertRaisesRegex(MODULE.SmokeError, "exact sha256"):
+                MODULE.platform_image(path, "linux/arm64", "API")
+
+
+if __name__ == "__main__":
+    unittest.main()