[SalesForce] Invocable Class – Test Class – Invalid type error

Ok, I first want to give full credit for original code designer Shane McLaughlin for creating a bunch of very useful process builder bolt-ons. They can be found here:
https://github.com/mshanemc/processBuilderBlocks

Now that I have given credit. I am trying to use his code to create an invocable class to handle public group membership. I was able to modify the main class but I am getting an error on the test class that I can't figure out. Can anyone help me out?

Main Class:

public with sharing class PB_AddToPublcGroup {

    @InvocableMethod(label='Add User to Public Group')
    public static void AddPublicGroup(list<AddGroupMember> requests) {

        list<string> output = new list<string>();

        for (AddGroupMember request:dedupe(requests)){
            //system.debug(request);
            //future methods can only accept primitives, so we serialize to a list of string
            output.add(JSON.serialize(request));
        }

        AddGroupsLater(output);

    }

    //what Process Builder/Flow Builder can reference for the input variables
    public class AddGroupMember {
        @InvocableVariable(required=true label='Public Group Name')
        public String PubGroupName;

        @InvocableVariable(required=true label='User Id')
        public Id UserId;
    }

    public static list<AddGroupMember> dedupe(list<AddGroupMember> input){
        set<AddGroupMember> temp = new set<AddGroupMember>(input);
        return new list<AddGroupMember>(temp);
    }

    //has to be handled as an @future transaction because the mixed DML issue!
    @future
    public static void AddGroupsLater (list<string> requests){
        list<GroupMember> gpMembers = new list<GroupMember>();

        for (string request:requests){

            //turn it back into the request object per Quinton Wall
            //https://developer.salesforce.com/blogs/developer-relations/2013/06/passing-objects-to-future-annotated-methods.html
            AddGroupMember APSR = (AddGroupMember)JSON.deserialize(request, AddGroupMember.class);
            Group groupId = [Select ID FROM Group WHERE Name = :APSR.PubGroupName];

            GroupMember groupMem = new GroupMember();
            groupMem.UserOrGroupId  = APSR.UserId;
            groupMem.GroupId        = groupId.Id;
            gpMembers.add(groupMem);
        }

        insert gpMembers;
    }

}

Test Class:

@istest
private class test_PB_Addons {

    //tests the class across a whole bunch of permissions being added.
    @isTest static void testPublicGroup() {
        integer userCount=5;
        //create users
        list<user> users = createUsers(userCount);
        //create a Public Group
        Group GP = createGroup();
        //create the inner class object and add to list
        list<PB_AddToPublicGroup.AddGroupMember> GMRs = new list<PB_AddToPublicGroup.AddGroupMember>();
        for (user u:users){
            PB_AddToPublicGroup.AddGroupMember GMR = new PB_AddToPublicGroup.AddGroupMember();
            GMR.UserId = u.id;
            GMR.PubGroupName = GP.Name;
            GMRs.add(GMR);
        }

        //call the invocable method
        test.startTest();
        PB_AddToPublicGroup.AddGroupMember(GMRs);
        test.stopTest();

        //asserts--check that user is in the group
        /*
list<PermissionSetAssignment> PSAs = [select Id, AssigneeId, PermissionSetId 
from PermissionSetAssignment
where AssigneeId in: users and PermissionSetId =: PS.Id];

system.assertEquals(userCount, PSAs.size()); 
*/
    }

    public static list<user> createUsers(integer numberOfUsers){
***Omitted****
    }

    private static Group createGroup(){
***Omitted***
    }
}

The error in test class is this line:

//create the inner class object and add to list

list<PB_AddToPublicGroup.AddGroupMember> GMRs = new list<PB_AddToPublicGroup.AddGroupMember>();

Error:

Invalid type: PB_AddToPublicGroup.AddGroupMember