fix: add signal rpc malformed-json regression test (#22995) (thanks @adhitShet)

src/signal/client.test.ts

@@ -0,0 +1,56 @@
+import { beforeEach, describe, expect, it, vi } from "vitest";
+
+const fetchWithTimeoutMock = vi.fn();
+const resolveFetchMock = vi.fn();
+
+vi.mock("../infra/fetch.js", () => ({
+  resolveFetch: (...args: unknown[]) => resolveFetchMock(...args),
+}));
+
+vi.mock("../infra/secure-random.js", () => ({
+  generateSecureUuid: () => "test-id",
+}));
+
+vi.mock("../utils/fetch-timeout.js", () => ({
+  fetchWithTimeout: (...args: unknown[]) => fetchWithTimeoutMock(...args),
+}));
+
+import { signalRpcRequest } from "./client.js";
+
+type ErrorWithCause = Error & { cause?: unknown };
+
+describe("signalRpcRequest", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    resolveFetchMock.mockReturnValue(vi.fn());
+  });
+
+  it("returns parsed RPC result", async () => {
+    fetchWithTimeoutMock.mockResolvedValueOnce(
+      new Response(
+        JSON.stringify({ jsonrpc: "2.0", result: { version: "0.13.22" }, id: "test-id" }),
+        {
+          status: 200,
+        },
+      ),
+    );
+
+    const result = await signalRpcRequest<{ version: string }>("version", undefined, {
+      baseUrl: "http://127.0.0.1:8080",
+    });
+
+    expect(result).toEqual({ version: "0.13.22" });
+  });
+
+  it("throws a wrapped error when RPC response JSON is malformed", async () => {
+    fetchWithTimeoutMock.mockResolvedValueOnce(new Response("not-json", { status: 502 }));
+
+    const err = (await signalRpcRequest("version", undefined, {
+      baseUrl: "http://127.0.0.1:8080",
+    }).catch((error: unknown) => error)) as ErrorWithCause;
+
+    expect(err).toBeInstanceOf(Error);
+    expect(err.message).toBe("Signal RPC returned malformed JSON (status 502)");
+    expect(err.cause).toBeInstanceOf(SyntaxError);
+  });
+});