title: Expected one assertion to be called but received zero
body: <p>I'm struggling with Jest, I just can't get it to work properly. </p>
  
  <p>Function I wanna test:</p>
  
  <pre><code>fetchPosts() {
      return new Promise((resolve, reject) =&gt; {
          Posts.find({}).then(posts =&gt; {
              if (posts) {
                  resolve(posts)
              } else {
                  reject("NOOOO")
              }
          })
      })
  }
  </code></pre>
  
  <p>Test:</p>
  
  <pre><code>describe('fetching posts', () =&gt; {
      it('should get a list of posts in Array format', () =&gt; {
        expect.assertions(1);
        const result = posts.fetchPosts();
        return expect(result).resolves.toEqual(expect.any(Array));
      })
  })
  </code></pre>
  
  <p>The <code>fetchPosts</code> function does return the whole list of posts. How can I make my test pass?</p>