I'm having trouble figuring out how to write test code for the following classes. They all seem very simple, but I'm a complete rookie to test code and am at a loss. I don't know if this will make sense to anybody but I wanted to see if I could get some help on these two classes :

public with sharing class Milestone1_TestProjectBuilder {

    public Integer numberMilestones { get; set; }
    public Integer numberTasks {get; set; }
    
    public void buildProject() {
        
        Milestone1_Project__c newProject = Milestone1_Test_Utility.sampleProjectActive('Sample ' + Datetime.now());
        insert newProject;
        
        for (Integer i=0; i < numberMilestones; i++) {
            Milestone1_Milestone__c ms = Milestone1_Test_Utility.sampleMilestone(newProject);
            insert ms;
            for (Integer j=0; j < numberTasks; j++) {
                Milestone1_Task__c task = Milestone1_Test_Utility.sampleTask(ms);
                insert task;
                
            }
        }
        
    }
}

and this one which are essentially just a field validation messages :

public with sharing class Milestone1_Move_Exception extends Exception{
    
    public static final String ERROR_MILESTONE_ALREADY_ASSIGNED_PROJECT = 'A milestone you are attempting to move is already assigned to this project. Please review your selection and try again.';
    public static final String ERROR_TASK_ALREADY_ASSIGNED_MILESTONE = 'A task you are attempting to move is already assigned to this milestone. Please review your selection and try again.';
    public static final String ERROR_MILESTONE_COMPLETE = 'Milestone is Complete, the Task can not be moved';
    public static final String ERROR_MILESTONE_HAS_SUCCESSORS = 'Top Level Milestone has successors and cannot be moved.  Redirect those successors and try again.';
    public static final String ERROR_MILESTONE_HAS_PREDECESSOR = 'Top Level Milestone has predecessor and cannot be moved.  Remove that predecessor and try again.';
    
    static testMethod void testConstants() 
    {
        //Just a place holder test method for static constants on this exception class.
        system.assert(true);
    }

}

As I'm sure you can tell, I'm a complete rookie to test code. I apologize for asking for help on this and not being able to at least give some. Thank you very much for your help and time.