Bun test / VitestでNext.jsのServer Actionsをテストする

sampleAction.bun.test.ts

import { describe, expect, mock, test } from "bun:test";
import { sampleAction } from "@/app/sampleAction";

describe("sampleAction", () => {
  test("正常：返り値が正しく返ってくる", async () => {
    const result = await sampleAction(true);
    expect(result).toEqual({ sampleAction: "sampleAction" });
  });

  test("異常：エラーページにリダイレクトされる", async () => {
    mock.module("next/navigation", () => {
      return {
        redirect: (path: string) => {
          return path;
        },
      };
    });
    const result = await sampleAction(false);
    // @ts-ignore redirectの返り値がunknownなので型エラーになってしまう。Bunでモジュールモックの呼び出し回数チェックできないのでこれで回避。
    expect(result).toBe("/error");
  });
});

sampleAction.ts

"use server";

import { redirect } from "next/navigation";

export async function sampleAction(flag = false) {
  if (flag) {
    return { sampleAction: "sampleAction" };
  }
  return redirect("/error");
}

sampleAction.vitest.test.ts

import { afterEach, describe, expect, test, vi } from "vitest";
import { sampleAction } from "./sampleAction";

describe("sampleAction", () => {
  test("正常：返り値が正しく返ってくる", async () => {
    const result = await sampleAction(true);
    expect(result).toEqual({ sampleAction: "sampleAction" });
  });

  test("異常：エラーページにリダイレクトされる", async () => {
    vi.mock("next/navigation", () => {
      return {
        redirect: (path: string) => {
          return path;
        },
      };
    });
    const result = await sampleAction(false);
    expect(result).toBe("/error");
  });
});