Fix multi-skeleton loading (#79)

* Add multi skeleton loading test

* Fix

sleap_io/io/slp.py

@@ -207,11 +207,11 @@ def read_skeletons(labels_path: str) -> list[Skeleton]:
 
         # Re-index correctly.
         skeleton_node_inds = [node["id"] for node in skel["nodes"]]
-        node_names = [node_names[i] for i in skeleton_node_inds]
+        sorted_node_names = [node_names[i] for i in skeleton_node_inds]
 
         # Create nodes.
         nodes = []
-        for name in node_names:
+        for name in sorted_node_names:
             nodes.append(Node(name=name))
 
         # Create edges.

tests/io/test_slp.py

@@ -186,3 +186,31 @@ def test_write_labels(centered_pair, slp_real_data, tmp_path):
         assert len(saved_labels.skeletons) == len(labels.skeletons) == 1
         assert saved_labels.skeleton.name == labels.skeleton.name
         assert saved_labels.skeleton.node_names == labels.skeleton.node_names
+
+
+def test_load_multi_skeleton(tmpdir):
+    """Test loading multiple skeletons from a single file."""
+    skel1 = Skeleton()
+    skel1.add_node(Node("n1"))
+    skel1.add_node(Node("n2"))
+    skel1.add_edge("n1", "n2")
+    skel1.add_symmetry("n1", "n2")
+
+    skel2 = Skeleton()
+    skel2.add_node(Node("n3"))
+    skel2.add_node(Node("n4"))
+    skel2.add_edge("n3", "n4")
+    skel2.add_symmetry("n3", "n4")
+
+    skels = [skel1, skel2]
+    labels = Labels(skeletons=skels)
+    write_metadata(tmpdir / "test.slp", labels)
+
+    loaded_skels = read_skeletons(tmpdir / "test.slp")
+    assert len(loaded_skels) == 2
+    assert loaded_skels[0].node_names == ["n1", "n2"]
+    assert loaded_skels[1].node_names == ["n3", "n4"]
+    assert loaded_skels[0].edge_inds == [(0, 1)]
+    assert loaded_skels[1].edge_inds == [(0, 1)]
+    assert loaded_skels[0].flipped_node_inds == [1, 0]
+    assert loaded_skels[1].flipped_node_inds == [1, 0]