How can I test Java method with pass value to another method?

I have getData method which takes 2 parameters. This method passes finalObject to another method and does not return anything. How can I test this method and the postforObjectmethod which takes input ?

Here is my method

private void getData(Set<Type> Types, Set<String> finalObject) {
    finalObject = Types.stream()
        .map(mark -> mark.getCurrentData())
        .filter(mark -> Enum1.getData().equals(mark)
        ||Enum2.getData().equals(mark))
        .map(tools -> tools.equals(Enum2.getData()) ? "Java" : tools)
        .collect(Collectors.toSet());
    postMethod(finalObject);
}