I have created a trigger, which generate's a random string, Please can any one help in writing the test class?

Question

trigger setGuid on dftly_app_contact__c (before insert) {
  For (dftly_app_contact__c dac: Trigger.new){
    Blob b = Crypto.GenerateAESKey(128);
    String h = EncodingUtil.ConvertTohex(b);
    String guid = h.SubString(0,8)+ '-' + 
                  h.SubString(8,12) + '-' + 
                  h.SubString(12,16) + '-' + 
                  h.SubString(16,20) + '-' + 
                  h.substring(20);
    system.debug(guid);
    dac.Guid_App_Contact__c = guid;
  }
}

Answer 1

The following code is an example of a test class for your Trigger. You will still have to write the actual assertions you want to do, i.e. whether the GUID string is the correct format.

If there's any required relations for dftly_app_contact__c, you will have to insert these records as well. You can do this simply inside your method or using testSetup: https://www.salesforce.com/us/developer/docs/apexcode/Content/apex_classes_annotation_testsetup.htm

@isTest
public class TestSetGuidTrigger {
    @isTest
    static void setGuid() {     
        dftly_app_contact__c dac = new dftly_app_contact__c();
        // SET ATTRIBUTES OF dftly_app_contact__c, IE NAME
        insert dac;

        dftly_app_contact__c dacTest = [SELECT Guid_App_Contact__c FROM dftly_app_contact__c WHERE Id =: dac];
        // USE System.assert() AND System.assertEquals() TO TEST WHETHER THE GUID FIELD IS SET AND WHETHER THE STRING IS IN THE RIGHT FORMAT
    }
}

Does that help?