How do we mock fetch for Redux Async Actions?

In the Writing Tests section of Redux,http://ift.tt/1WuLEat, how does the store.dispatch(actions.fetchTodos()) not invoke the fetch method, if store.dispatch is literally calling actions.fetchTodos?

it('creates FETCH_TODOS_SUCCESS when fetching todos has been done', (done) => {
    nock('http://example.com/')
      .get('/todos')
      .reply(200, { todos: ['do something'] })

const expectedActions = [
  { type: types.FETCH_TODOS_REQUEST },
  { type: types.FETCH_TODOS_SUCCESS, body: { todos: ['do something']  } }
]
const store = mockStore({ todos: [] }, expectedActions, done)
store.dispatch(actions.fetchTodos())


})