Verify NonPublic method with Predicate as argument

I'm not sure that I fully understand the problem.

Bar is a private static method with a predicate argument.

public class Foo
{
    public static void BarWrapper()
    {
        int b = 1;
        Bar(a => a > b);
    }

    private static void Bar(Predicate<int> a)
    {
    }
}

Here I call BarWrapper which calls Bar.
I first fake bar using callOriginal, tos signal Isolator to track this method, then verify it wascalled.

[TestMethod]
public void TestMethod1()
{
    Isolate.NonPublic.WhenCalled(typeof(Foo), "Bar").CallOriginal();

    Foo.BarWrapper();

    Isolate.Verify.NonPublic.WasCalled(typeof(Foo), "Bar");
}

Let me know if this is the case post an example of your code.