Testing Redux combined reducers

Say I have several reducer functions and I combine them all into one reducer using combineReducers(...), is there a way of testing what reducers the combined reducer actually contains?

For example, if I have this:

import { combineReducers } from 'redux'

const reducer1 = (state, action) => {...}
... (more reducers, etc)

const rootReducer = combineReducers({
    reducer1,
    reducer2,
    reducer3
})

export default rootReducer

Can I write a test with Mocha and Expect.js that will enable me to check if the rootReducer contains say reducer2? Is this even possible?

The way I currently have my project set up is that each reducer is in a separate file and is then imported into the file where the combineReducers(...) function is used to combine them all. I am testing all the individual reducers to check that they do what they should, but I also thought it would be a good idea to test the combined reducer to make sure that it contains all the other reducers that it should (in case I forget to add one for example).

Thanks