user.actions.js

export function fetchUser(id) {
  return (dispatch, getState, {analytics, api}) => {
    return api.fetchUser().then(user => {
      analytics.track(...);
    })
  }
}

user.actions.spec.js

import {fetchUser} from './user.actions';

describe('fetchUser', () => {
  it('should fetch user', () => {
    fetchUser('1')(mockDispatch, mockGetState, {api: mockApi, analytics: mockAnalytics});
    /* your assertions */
  })
})