Hi,
From what I understand, you are trying to invoke the constructor yet ignoring the private method that's called in it.
In this case, there is no reason to fake the constructor, as soon as you create an instance of the object the constructor will be called.
all that's left to do is to make sure that the private method will be ignored and finally verify that the "Foo" method wasn't called.
For example, you can see the following test:
[TestMethod]
public void ClassWithConstructor() {
var real = new MyClass();
Isolate.NonPublic.WhenCalled(real,"Foo").IgnoreCall();
Isolate.Verify.NonPublic.WasNotCalled(real, "Foo");
}
If that was not your attention please describe it in more details and we will be glad to help.