Unit Testing in ASP.NET Web forms

I a developing a project which is OnlineVideoStreaming website. Its in ASP.NET web forms.

I want to unit test some of the functionalities such as login, registration etc. But the problem is how to test the code such as button click event in which login code is written in code behind.?

What parameters to pass in "object sender and eventargs e"?

 

Example:

 

public void btn_click(object sender,eventargs e)

{

   // Login code here 

}