This C# does not need to be compiled into a .dll, it's a .csx file that is compiled at runtime by the Roslyn api. The expression lambda is populated by Selenium webdriver code.

FunctionalWebTest.cs

ExpectedResult = true;
ScriptResult = (new WebInteraction(
  
  WithBrowser: WebInteraction.FireFox,
  Script: (w) =>
  {
    // Selenium webdriver code
    w.Driver.Navigate().GoToUrl("https://duckduckgo.com/");
    
    w.Wait
    .Until(p => p.FindElement(By.Name("q")));
    
    w.Driver
    .FindElement(By.Name("q"))
    .SendKeys("I don't wanna be a playa no mo");
    
    w.Result = true;  
  
  }))
  .Execute()
  .Result;