From 9ae30bd412c504adc0bb845232a9ae5cacd66896 Mon Sep 17 00:00:00 2001
From: Igor Velho <velhoi@ryanair.com>
Date: Mon, 24 Aug 2026 14:47:59 +0100
Subject: [PATCH] test: add computeSubtreeCost coverage (flat, nested, cycle,
 zero-cost, unknown id)

---
 .../chat/work-status/subagentCost.test.ts     | 49 ++++++++++++++++++-
 1 file changed, 48 insertions(+), 1 deletion(-)

diff --git a/packages/ui/src/components/chat/work-status/subagentCost.test.ts b/packages/ui/src/components/chat/work-status/subagentCost.test.ts
index 8c3fbeb3..059f2724 100644
--- a/packages/ui/src/components/chat/work-status/subagentCost.test.ts
+++ b/packages/ui/src/components/chat/work-status/subagentCost.test.ts
@@ -1,6 +1,6 @@
 import { describe, expect, test } from 'bun:test';
 import type { Session } from '@opencode-ai/sdk/v2';
-import { buildChildrenIndex, formatCost } from './subagentCost';
+import { buildChildrenIndex, computeSubtreeCost, formatCost } from './subagentCost';
 
 function makeSession(id: string, cost: number, parentID?: string): Session {
   return { id, cost, parentID } as unknown as Session;
@@ -23,3 +23,50 @@ describe('formatCost', () => {
     expect(formatCost(2)).toBe('$2');
   });
 });
+
+describe('computeSubtreeCost', () => {
+  test('sums a flat root with two direct children', () => {
+    const root = makeSession('root', 1);
+    const childA = makeSession('a', 2, 'root');
+    const childB = makeSession('b', 3, 'root');
+    const sessions = [root, childA, childB];
+    const sessionsById = new Map(sessions.map((s) => [s.id, s]));
+    const childrenByParent = buildChildrenIndex(sessions);
+    expect(computeSubtreeCost('root', sessionsById, childrenByParent)).toBe(6);
+  });
+
+  test('rolls up cost through nested descendants', () => {
+    const root = makeSession('root', 1);
+    const child = makeSession('child', 2, 'root');
+    const grandchild = makeSession('grandchild', 4, 'child');
+    const sessions = [root, child, grandchild];
+    const sessionsById = new Map(sessions.map((s) => [s.id, s]));
+    const childrenByParent = buildChildrenIndex(sessions);
+    expect(computeSubtreeCost('root', sessionsById, childrenByParent)).toBe(7);
+    expect(computeSubtreeCost('child', sessionsById, childrenByParent)).toBe(6);
+  });
+
+  test('does not double-count or infinite-loop on a cycle', () => {
+    const a = makeSession('a', 1, 'b');
+    const b = makeSession('b', 2, 'a');
+    const sessions = [a, b];
+    const sessionsById = new Map(sessions.map((s) => [s.id, s]));
+    const childrenByParent = buildChildrenIndex(sessions);
+    expect(computeSubtreeCost('a', sessionsById, childrenByParent)).toBe(3);
+  });
+
+  test('treats zero and undefined cost as zero, not a break', () => {
+    const root = makeSession('root', 0);
+    const child = { id: 'child', parentID: 'root' } as unknown as Session;
+    const sessions = [root, child];
+    const sessionsById = new Map(sessions.map((s) => [s.id, s]));
+    const childrenByParent = buildChildrenIndex(sessions);
+    expect(computeSubtreeCost('root', sessionsById, childrenByParent)).toBe(0);
+  });
+
+  test('returns 0 for an unknown id', () => {
+    const sessionsById = new Map<string, Session>();
+    const childrenByParent = new Map<string, Session[]>();
+    expect(computeSubtreeCost('missing', sessionsById, childrenByParent)).toBe(0);
+  });
+});