test: add inventory unit tests

tests/__init__.py

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+# pytest package marker

tests/test_inventory.py

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+import json
+import tempfile
+from pathlib import Path
+
+import pytest
+
+from metis.pkg import inventory
+
+def test_load_and_find_node():
+    data = {
+        "classes": [
+            {
+                "name": "rpi5",
+                "arch": "arm64",
+                "os": "ubuntu",
+                "image": "file:///tmp/base.img",
+                "checksum": "sha256:deadbeef",
+                "default_labels": {"hardware": "rpi5"},
+            }
+        ],
+        "nodes": [
+            {
+                "name": "titan-04",
+                "class": "rpi5",
+                "hostname": "titan-04",
+                "ip": "192.168.22.30",
+                "k3s_role": "agent",
+            }
+        ],
+    }
+    with tempfile.TemporaryDirectory() as tmp:
+        path = Path(tmp) / "inv.yaml"
+        path.write_text(json.dumps(data))
+        inv = inventory.Load(path)
+        node, cls, err = inv.FindNode("titan-04")
+        assert err is None
+        assert node.Hostname == "titan-04"
+        assert cls.Arch == "arm64"
+
+
+def test_find_node_missing():
+    inv = inventory.Inventory(classes=[], nodes=[])
+    node, cls, err = inv.FindNode("missing")
+    assert err is not None
+    assert node is None
+    assert cls is None