@SafeVarargs
    public final OrderTester<T> areLessThan(T... group) {
        return addGroup(group);
    }
Add group of objects being "less" (wrt. compareTo) than all the objects which follow.
@param group group of objects
@return the {@link OrderTester} instance, for method chaining
testutil/src/main/java/com/yahoo/test/OrderTester.java