How to verify that a method of a SUT has been called?

Question

let's say I have this class

public class MyClass
{
    public void InnerMethod(){}

    public void OuterMethod(SomeType sameValue)
    {
       if(someCondition)
       {
          InnerMethod(); 
       }
       else
       {
         ...
       }
    }
}

I want to check that the InnerMethod was called

[Fact]
public void CanDoSomething()
{
   var sut = new MyClass();
   sut.OuterMethod(someValue);

  //Assert that InnerMethod was called
}

If InnerMethod belonged to a mocked object, I would have just called mockObject.Verify(x => x.InnerMethod);. However, InnerMethod is a concrete method belonging to the sut itself.

How to check that InnerMethod was called.

Thanks for helping.