inner call unit test with Enzyme and Sinon

I am trying to write the test for the function with an inner call in enzyme and Sinon, but I encounter some issues about the inner call.

Here is my code:

Chat.js

sendMssage = text => {
    const { user } = this.props;
    let message = this.messageModel.normalize(text);

    this.socketClient.onSendMessage(message, user);
    this.addMessage(message);
  };

test.js

  it('should call sendMessage function', () => {
    const wrapper = shallow(<ChatWindow />);
    const instance = wrapper.instance();
    sinon.spy(instance.socketClient(
    message,
    user,
  ));
    socketClicent.onSendMessage(message, user);
    Instance.sendMessage(message);
  });

It throws an error:

instance.socketClient is not a function

Can anybody help me out understand what am I doing wrong?