KuttnerModel object checkTests whether the input object is a valid object of class KuttnerModel.
is.KuttnerModel(object, return.logical = FALSE)A logical value or nothing, depending on the value of return.logical.
An object to be tested.
If return.logical = FALSE (default), an error message is printed
if the object is not of class KuttnerModel. If return.logical = TRUE, a logical
value is returned.