store.dispatch cannot read property 'then' of undefined

I am trying to test my async action and I get this error: store.dispatch cannot read property 'then' of undefined

I tried to use the then on the actionTypes (I am sorry, that is an actionCreator but I imported it as actionType), but it goes from undefined to TypeError: actionTypes.fetchGitHubDataAsync(...).then is not a function.

        // Response body sample
        const mockData = [
          {
              "name": "javascript",
              "display_name": "JavaScript",
              "short_description": "JavaScript (JS) is a lightweight interpreted programming language with first-class functions.",
              "description": "JavaScript (JS) is a lightweight interpreted or JIT-compiled programming language with first-class functions. While it is most well-known as the scripting language for Web pages, many non-browser environments also use it, such as Node.js, Apache CouchDB and Adobe Acrobat. JavaScript is a prototype-based, multi-paradigm, dynamic language, supporting object-oriented, imperative, and declarative (e.g. functional programming) styles.",
              "created_by": "Brendan Eich",
              "released": "December 4, 1995",
              "created_at": "2016-11-28T18:41:00Z",
              "updated_at": "2019-11-06T15:05:24Z",
              "featured": true,
              "curated": true,
              "score": 7954.724
            }
      ]

        fetchMock.getOnce('https://api.github.com/search/topics?q=javascript',
                { body: { results: mockData }})

        const expectedActions = [
         { type: actionTypes.FETCH_GITHUB_DATA},
        ]
        store.dispatch(actionTypes.fetchGitHubDataAsync())
             .then(() => {
                 expect(store.getActions()).toEqual(expectedActions)
             })
    })```