Someone on the forum was gracious enough to help me with the below code. Basically, it checks if a case is closed and there is incoming email, it will then clone the case.

Problem is how can I replicate an incoming message in a test class to test the trigger. I can create the new case and change its status to closed with the close, but would be the best way to replicate a new incoming email in the code. Is there an incoming email flag.

Thanks in advance.

trigger AutoCloneCase on EmailMessage (after insert) {
Set<ID> caseSet = new Set<ID>();
List<Case>cloneList = new List<Case>();
for (EmailMessage so : Trigger.new) {
    if(((String)so.parentid).startsWith('500') && so.Incoming){
        caseSet.add(so.parentid); 
    } 
}
Map<Id,case> caseMAP = new Map<Id,case>([SELECT id, isClosed, Type, Auto_Closed__c FROM Case WHERE id in:caseSet]);  
for(Case c:caseMAP.values()){
    if(c.IsClosed && c.Type == 'Support' && c.Auto_Closed__c == true) {
        Case cloneCase = c.clone(false,true);
        cloneCase.parentid=c.id;  
        cloneList.add(cloneCase);
    }
}
try { 
    insert cloneList;      
} catch(DMLException e) {   
     System.debug('The following exception has occurred: ' + e.getMessage()); 
}
}

Then for the test.

@isTest(seeAllData=true)
private class TestSupportTrigger{
static testMethod void myUnitTest() {      
    Case c = new Case(Severity__c = '4 (General Support)',  Origin = 'Self Service   Portal', Subject = 'Unit Test', Type = 'Support', Status = 'Closed', Time_Spent__c = 5, Auto_Closed__C = true );
    insert c;

    EmailMessage[] newEmail = new EmailMessage[0];
    newEmail.add(new EmailMessage(FromAddress = '[email protected]', Incoming = True, ToAddress= '[email protected]', Subject = 'Test email', TextBody = 'Test', ParentId = c.Id)); 

    Test.startTest();     
    insert newEmail;
    Test.stopTest();         
}
}