使用Typescript和Sinon在单例类中测试静态方法

Question

I have a DAO class as a separate layer for getting data from my repository. I made the class Singleton and methods static.

In another class I made other service methods for transforming the data. I would like to write tests for this code but don't succeed.

How to mock the Dao repository methods?

This is what I tried so far:

// error: TS2345: Argument of type "getAllPosts" is not assignable to paramenter of type "prototype" | "getInstance"
const dao = sinon.stub(Dao, "getAllPosts");

// TypeError: Attempted to wrap undefined property getAllPosts as function
const instance = sinon.mock(Dao);
instance.expects("getAllPosts").returns(data);

export class Dao {

    private noPostFound: string = "No post found with id";
    private dbSaveError: string = "Error saving to database";

    public static getInstance(): Dao {
        if (!Dao.instance) {
            Dao.instance = new Dao();
        }
        return Dao.instance;
    }

    private static instance: Dao;
    private id: number;
    private posts: Post[];

    private constructor() {
        this.posts = posts;
        this.id = this.posts.length;
    }

    public getPostById = (id: number): Post => {
        const post: Post = this.posts.find((post: Post) => {
            return post.id === id;
        });

        if (!post) {
            throw new Error(`${this.noPostFound} ${id}`);
        }
        else {
            return post;
        }
    }

    public getAllPosts = (): Post[] => {
        return this.posts;
    }

    public savePost = (post: Post): void => {
        post.id = this.getId();

        try {
            this.posts.push(post);
        }
        catch(e) {
            throw new Error(this.dbSaveError);
        }
    }
}

Answer 1

Solved it like this:

// create an instance of Singleton
const instance = Dao.getInstance();

// mock the instance
const mock = sinon.mock(instance);

// mock "getAllPosts" method
mock.expects("getAllPosts").returns(data);