diff --git a/frontend/src/setupTests.ts b/frontend/src/setupTests.ts
index 3de2908..0f1a560 100644
--- a/frontend/src/setupTests.ts
+++ b/frontend/src/setupTests.ts
@@ -7,8 +7,14 @@ import { beforeEach, vi } from "vitest";
 beforeEach(() => {
 	vi.stubGlobal(
 		"fetch",
-		vi.fn(() =>
-			Promise.resolve(new Response(JSON.stringify({}), { status: 200 })),
-		),
+		vi.fn((input: string | URL | Request) => {
+			const url = typeof input === "string" ? input : input.toString();
+			// Endpoints that return arrays need [] not {} to avoid "not iterable" errors.
+			const arrayEndpoints = ["/agents", "/agents/config"];
+			const body = arrayEndpoints.some((ep) => url.endsWith(ep))
+				? JSON.stringify([])
+				: JSON.stringify({});
+			return Promise.resolve(new Response(body, { status: 200 }));
+		}),
 	);
 });