test: cover shared snapshot ancestor traversal

Author: thymikee

src/utils/__tests__/snapshot-processing.test.ts

@@ -0,0 +1,42 @@
+import { test } from 'vitest';
+import assert from 'node:assert/strict';
+import {
+  buildSnapshotNodeByIndex,
+  findNearestAncestor,
+  findSnapshotAncestor,
+} from '../snapshot-processing.ts';
+import type { SnapshotNode } from '../snapshot.ts';
+
+test('findSnapshotAncestor walks non-contiguous parent indexes until resolver returns a value', () => {
+  const nodes: SnapshotNode[] = [
+    { ref: 'e10', index: 10, type: 'Window' },
+    { ref: 'e30', index: 30, parentIndex: 20, type: 'Text' },
+    { ref: 'e20', index: 20, parentIndex: 10, type: 'Cell' },
+  ];
+  const visited: number[] = [];
+
+  const ancestor = findSnapshotAncestor(
+    nodes,
+    nodes[1]!,
+    buildSnapshotNodeByIndex(nodes),
+    (node) => {
+      visited.push(node.index);
+      return node.type === 'Window' ? node : null;
+    },
+  );
+
+  assert.deepEqual(visited, [20, 10]);
+  assert.equal(ancestor?.index, 10);
+});
+
+test('findNearestAncestor resolves parents by snapshot index rather than array position', () => {
+  const nodes: SnapshotNode[] = [
+    { ref: 'e10', index: 10, type: 'Window' },
+    { ref: 'e30', index: 30, parentIndex: 20, type: 'Text' },
+    { ref: 'e20', index: 20, parentIndex: 10, type: 'Cell' },
+  ];
+
+  const ancestor = findNearestAncestor(nodes, nodes[1]!, (node) => node.type === 'Window');
+
+  assert.equal(ancestor?.index, 10);
+});

src/utils/snapshot-processing.ts

@@ -109,6 +109,11 @@ export function buildSnapshotNodeByIndex(nodes: SnapshotState['nodes']): Map<num
   return new Map(nodes.map((candidate) => [candidate.index, candidate]));
 }
 
+/**
+ * Walks from the given node through its parent chain and returns the first
+ * non-null value produced by `resolve`. Returning null from `resolve` skips
+ * that ancestor and continues walking toward the root.
+ */
 export function findSnapshotAncestor<T>(
   nodes: SnapshotState['nodes'],
   node: SnapshotNode,
@@ -140,6 +145,9 @@ export function isDescendantOfSnapshotNode(
   );
 }
 
+/**
+ * Returns the nearest ancestor matching `predicate`; false means keep walking.
+ */
 export function findNearestAncestor(
   nodes: SnapshotState['nodes'],
   node: SnapshotState['nodes'][number],