code: private List<VarDef> getVarsRemaining( Iterator<VarDef> vars, final TestCaseDef testCase)
      {
      return
        IteratorUtils.toList(
          IteratorUtils.filteredIterator(
            vars,
            var -> testCase.getBinding( var) == null));
      }
docs: Returns the members of the given set of input variables not bound by the given test case.