reducer.js

// reducer.js
export const initialState = {
  authenticated: false,
  authenticating: false,
};

export const loginReducer = (
  state = initialState,
  action
) => {
  switch (action.type) {
    case AUTHENTICATION.AUTHENTICATED:
      return { ...state, authenticating: false, authenticated: action.payload.authenticated };
    default:
      return state;
  }
};

// action.js
export const switchAuthenticatedFlag = status => {
  return {
    type: 'LOGIN/AUTHENTICATED',
    payload: {
      authenticated: status,
    },
  };
};

// reducer.test.js
describe('Login Reducers', () => {
  it('properly captures a dispatch to change authenticated state', () => {
    expect(loginReducer(initialState, switchAuthenticatedFlag(true)))
      .toEqual({
        authenticated: true,
        authenticating: false,
      });
  });
})