How to test the file uploading function for react-dropzone

I want to test my react dropzone onDrop method, here is what I've tried so far.

describe("RoadOrders", () => {
  let props;
  let mountedRoadOrders;
  const roadOrders = () => {
    if (!mountedRoadOrders) {
      mountedRoadOrders = mount(
        <MuiThemeProvider muiTheme={getMuiTheme()}>
          <Provider store={store}>
          <RoadOrders {...props} />
          </Provider>
        </MuiThemeProvider>
      );
    }
    return mountedRoadOrders;
  }

  beforeEach(() => {
    props = {};
    mountedRoadOrders = undefined;
  });

  describe("when dropped file", () => {
    beforeEach(() => {
      props.uploadFiles = undefined;
    });

    it("should upload that file to firebase", () => {
      const uploadFiles = roadOrders().find("Dropzone");
      uploadFiles.simulate('drop', {
        target: {
          files: [
            'a.jpg',
            'b.jpg',
            'c.jpg'
          ]
        }
      })
      expect(roadOrders()).toBe(1);
    });
  });
});

It seems the onDrop function did triggered, but the files weren't successfully uploaded to the cloud. How can I test the file uploading function and check the callback from the server to see if they were passed to the server?