public void IteratorNegativeNN() {
   var test2 = new CodeUnderTest.IteratorSimpleContract.Test2();
   test2.Test1a(null); // Precondition of Test1a violated.
 }
 public void IteratorPositiveNN() {
   var test2 = new CodeUnderTest.IteratorSimpleContract.Test2();
   test2.Test1a("hello"); // Precondition of Test1a holds
 }