Business Layer/Data Layer architecture,Test Driven Development and MVC

Using Test Driven Development (TDD) with ASP.NET can be a messy process if your not aware of some pitfalls.  Say you wrote a button click event handler that does a couple of string conversions before calling the business layer:  protected void Button1_Click(object sender, EventArgs e) {      string aString =     //Do some string conversions      BusinessLayer bl = [...]