test-middleware.js

const next = jest.fn();
const baseAction = {
  type: OrderDetailsActionConstants.INITIATE_ORDER_DETAILS_RETRIEVAL,
  orderId: 'orderId',
  patientId: 'patientId',
  encounterId: 'encounterId'
};
const action = Object.assign({}, baseAction, toRemove: 'toRemove');
  
serializeInitiateOrderDetailsRetrievalAction()(next)(action);

expect(next.mock.calls.length).toBe(1);
expect(next.mock.calls[0].length).toBe(1);
expect(next.mock.calls[0][0]).toEqual(baseAction);