There’s no valid reason to test this with is. The only plausible explanation for such a test is that you’re executing code in a parent class conditionally based on the kind of child class this is. But code that’s specific to a child class should be in that child class, not in the parent.

Noncompliant Code Example

public class JunkFood
{
  public void DoSomething()
  {
    if (this is Pizza) // Noncompliant
    {
      // ...
    } else if (...
  }
}