如何在 Jest 中使用 Mocked 对象作为参数来模拟从静态方法创建的对象答案

【问题标题】：How mock an object created from a static method with a Mocked objet as param in Jest如何在 Jest 中使用 Mocked 对象作为参数来模拟从静态方法创建的对象
【发布时间】：2021-05-23 12:30:44
【问题描述】：

我写了一个 Nestjs 示例项目，项目源代码：https://github.com/hantsy/nestjs-graphql-sample 并尝试测试自定义权限保护。

@Injectable()
export class HasPermissionsGuard implements CanActivate {
  constructor(private readonly reflector: Reflector) {}
  canActivate(
    context: ExecutionContext,
  ): boolean | Promise<boolean> | Observable<boolean> {
    const routePermissions = this.reflector.get<PermissionType[]>(
      HAS_PERMISSIONS_KEY,
      context.getHandler(),
    );
    if (!routePermissions || routePermissions.length == 0) {
      return true;
    }
    const { user } = GqlExecutionContext.create(context).getContext()
      .req as AuthenticatedRequest;
    return (
      user.permissions &&
      user.permissions.some((r) => routePermissions.includes(r))
    );
  }
}

当我尝试用Jest测试HasPermissionsGuard的逻辑时，

  it('should return true if the `HasPermissions` decorator is set', async () => {
    const context = mock<ExecutionContext>();
    context.getHandler.mockReturnValue({} as any);

    // the following will failed. 
    const host = mock<ExecutionContextHost>();
    host.getArgByIndex.mockImplementation((idx: number) => {
      return {
        req: { user: { permissions: [PermissionType.WRITE_POSTS] } as any },
      } as any;
    });

    const ctx = mock<GqlExecutionContext>();
    ctx.getContext.mockReturnValue({
      req: { user: { permissions: [PermissionType.WRITE_POSTS] } as any },
    });

    reflecter.get
      .mockReturnValue([PermissionType.WRITE_POSTS])
      .calledWith(HAS_PERMISSIONS_KEY, context.getHandler());

    const result = await guard.canActivate(context);

    expect(result).toBeTruthy();
    expect(reflecter.get).toBeCalledTimes(1);
  });

我使用了jest-mock-extended和jest，如何模拟GqlExecutionContext.create(context).getContext()？

【问题讨论】：

标签： jestjs nestjs

【解决方案1】：

自己解决了。创建一个模拟函数并将其分配给create 静态方法。

    const mockedCreate = jest
      .fn()
      .mockImplementation((ctx: ExecutionContext) => {
        return {
          getContext: jest.fn().mockReturnValue({
            req: {
              user: { permissions: [PermissionType.WRITE_POSTS] } as any,
            } as any,
          }),
        } as any;
      });
    GqlExecutionContext.create = mockedCreate;

【讨论】：