code: private List<TestCaseDef> getBaseValidCases( FunctionInputDef inputDef, VarTupleSet validTuples, List<TestCaseDef> baseCases)
      {
      logger_.debug( "{}: Extending valid base test cases", inputDef);
  
      Iterator<TestCaseDef> validBaseCases =
        IteratorUtils.filteredIterator(
          baseCases.iterator(),
          testCase -> testCase.getInvalidVar() == null);
  
      List<TestCaseDef> testCases = extendBaseCases( inputDef, validTuples, validBaseCases);
  
      logger_.info( "{}: Extended {} valid base test cases", inputDef, testCases.size());
      return testCases;
     }
docs: Returns a set of valid {@link TestCaseDef test case definitions} that extend the given base test cases.