How to mock vuex functions with no direct access? - vue.js

Question

So I have run into quite a test problem.
To Summarize:
A while back I created a private npm Module, that manages and create a vuex store and injects it as a module into the main vuex store.
Now I want to mock a specific function of that vuex module in my test but that doesn't work.
I tried this:
store.getters.getSomething = jest.fn(() => "stuff);
But that results in this error:
TypeError: Cannot set property getSomething of #<Object> which has only a getter
Now did a little digging, and I here you can see where this getter comes from:
First there is a simple vuex module definition:
//vuexModule this is not accessible outside of the npm module
getters:{
getSomething: (state)=>{ return "stuff"}
}
export { getters }
Now this is imported into this class:
//storeProvider //this is exposed by the npm package
import vuexModule from "./vuexModule";
export default class StoreProvider {
constructor(vuexStore, vuexModuleName = "someStore") {
this.vuexStore = vuexStore;
this.vuexStore.registerModule(vuexModuleName, VuexConfigStore);
}
So this class will generate a vuex module using the previously defined module.
Now the whole thing is added to the main vuex store in the actual application.
Note: this code is now the actual application and not in the npm package.
import StoreProvider from "someNpmModule";
import mainStore from "vuexPlugin";
const storeProvider = new StoreProvider(store);
//later in main:
new Vue({ mainStore })
So the question is: How can I mock getSomething?
I know the code is quite abstracted, but I can't show all the code, and its probably too much for stackoverflow.
The main point is, that I can just import the getter and mock it like this:
import {getSomething} from "...";
getSomething = jest.fn(() => "stuff);
//Or this:
store.getters.getSomething = jest.fn(() => "stuff);
I found this stackoverflow question: TypeError during Jest's spyOn: Cannot set property getRequest of #<Object> which has only a getter
But as the npm package is rather big I can't just mock the whole package for the unit tests, as it provides some necessary pre-conditions. I tried genMockFromModule(), but I still need to target this specific function.
And as mentioned I can't simply import the function.
Any ideas?