React testing use mockstore with custom store to test it

I would like to test components that are using redux store in my project. Here is the function that I use fo getting some store elements:

const variable = store.getState().serverConfiguration.testValue;

When I am testing this component I use mockStore to do that so my store is empty right? That is why I get error saying that TypeError: Cannot read property 'testValue' of undefined

Is there a way to pass my custom store to mockStore so that it will be possible to test it correctly? I tried to do that like this but it doesn't work:

const store = configureMockStore()({
serverConfiguration: {
    testValue: "Admin"
}

});