I've tried two bits of code now and I keep getting the error:

Challenge not yet complete in My Trailhead Playground 3
The 'challengeComplete' method in the 'UnitOfWorkTest' class has not successfully passed all tests. Ensure that you run the tests and it passes successfully before attempting this challenge again.

Here's the code I'm trying to run:

//Code attempt #2
public class UnitOfWorkTest {
    public static void challengeComplete() {
        fflib_SObjectUnitOfWork uow = new fflib_SObjectUnitOfWork(
            new Schema.SObjectType[]{
                Account.SObjectType,
                Contact.SObjectType, 
                Note.SObjectType});
        for (Integer i = 0; i < 100; i++) {
            Account acc = new Account(Name = 'TestAcc' + i);
            uow.registerNew(acc);
            for (Integer j = 0; j < 5; j++) {
                Contact c = new Contact(LastName = 'TestContact' + i + '_' + j);
                uow.registerNew(c, Contact.AccountId, acc);
                Note n = new Note(Title = 'TestNote' + i + '_' + j, Body = 'Test note body.');
                uow.registerNew(n, Note.ParentId, acc);
            }
        }
        uow.commitWork();
        System.assertEquals(100, [SELECT Id from Account].size());
        System.assertEquals(500, [SELECT Id from Contact].size());
        System.assertEquals(500, [SELECT Id From Note].size());
    }
}
/*My Original Code, attempt #1
public class UnitOfWorkTest {
    public static void challengeComplete(){
        //Create the unit of work
        fflib_SObjectUnitOfWork uow = new fflib_SObjectUnitOfWork(
            new Schema.SObjectType[]{
                Account.SObjectType,
                Contact.SObjectType,
                Note.SObjectType
            }
        );
        //Do Some Work!
        for(Integer a=[select id from account].size(); a<100; a++){
            Account acc = new Account();
            acc.Name = 'UoW Test Name' + a;
            uow.registerNew(acc);
            for(Integer c=0; c<5; c++){
                Contact cont = new Contact();
                cont.FirstName = 'James ';
                cont.LastName = acc.name + c;
                uow.registernew(cont, Contact.AccountId, acc);
                Note nt = new Note();
                nt.title = 'UoW Note #' + c;
                nt.Body = 'UoW Body ' + c;
                uow.registernew(nt, Note.ParentId, acc);
            }
        }
        //Commit the work to the database
        uow.commitWork();
        
        System.assertEquals(100, [select id from account].size());
        System.assertEquals(500, [select id from contact].size());
        System.assertEquals(500, [select id from note].size());
    }
}
*/