Update_Current_Job_Title_Test

Update_Current_Job_Title_Test

// Assuming trigger is:
trigger Update_Current_job_Title_onContact on Career_Path__c (After insert, After update) {

    if((trigger.isInsert || trigger.isUpdate) && trigger.isAfter)
    {
        Update_Current_Job_Title.WhenInsertNewCareerPathOrUpdate(trigger.new);
    }

}

// Assuming class is:
public class Update_Current_Job_Title {


    public static void WhenInsertNewCareerPathOrUpdate(List<Career_Path__c> careerPathListNew)
    {
        try{
        List<Career_Path__c> careerPathList = new  List<Career_Path__c>();
        List<contact> contactList = new List<contact>();
        List<contact> contactListUpdated = new List<contact>();
        set<id> IdList = new set<Id>();
        careerPathList = [select id, contact__c , Job_title_2__c,Current__c 
                          from Career_Path__c
                          where id in:careerPathListNew
                          and Job_title_2__c !=null];
                          
            for(Career_Path__c cp :careerPathList )
            {
                IdList.add(cp.contact__c);
            }

            contactList = [select id, Current_Job_Title__c from contact where id in : IdList];

            for(Career_Path__c cpp :careerPathList )
              {
                for(contact cc :contactList )
                {
                  if(cpp.Contact__c == cc.id && cpp.Current__c==true)
                  {
                    cc.Current_Job_Title__c = cpp.Job_Title_2__c;
                    contactListUpdated.add(cc);
                  }
                }   
            }    
            update contactListUpdated;
    } catch(Exception e)
    {
        system.debug('Error is -> '+ e.getMessage() + 'at Line -> '+ e.getLineNumber());
    }
  }
}

// Then a test class that 'covers' 75% of the lines of your code is required.
// By 'covers', we mean 'uses'. That's all that's technically required. Some test code that makes use of your code.
// So, what does that look like? Well, the simplest version for us here is creating and updating a Career_Path__c record.
// We know that our trigger fires every time we insert and update a record, so we can start there:
@isTest
private class Update_Current_Job_Title_Test {

  static testMethod void testInsertAndUpdate() {
  
    // Given
    Contact__c contact = new Contact__c(
      Current_Job_Title__c = 'oldTitle'
    );
    insert contact;
    
    Career_Path__c careerPath = new Career_Path__c (
      Contact__c = contact.Id,
      Job_Title_2__c = 'newTitle'
    );
    insert careerPath;
    
    // When    
    careerPath.Current__c = true;
    update careerPath;
    
  }
}

// There's one major problem with this test class. 
// Even if it works, and covers 75% of your code, it doesn't 'know' that it works.
// All it checks is that it didn't fail so badly that an Exception was thrown.
// So, we include a 'then' condition. Something that asserts our code did what we intended.
// Specifically, we need to check if the all the related Contact__c records have had their Job Title updated.
@isTest
private class Update_Current_Job_Title_Test {

  static testMethod void testInsertAndUpdate() {
  
    // Given
    Contact__c contact = new Contact__c(
      Current_Job_Title__c = 'oldTitle'
    );
    insert contact;
    
    Career_Path__c careerPath = new Career_Path__c (
      Contact__c = contact.Id,
      Job_Title_2__c = 'newTitle'
    );
    insert careerPath;
    
    // When    
    careerPath.Current__c = true;
    update careerPath;
    
    // Then
    contact = [SELECT Current_Job_Title__c FROM Contact__c WHERE Id :contact.Id LIMIT 1];
    System.assertEquals('newTitle', contact.Current_Job_Title__c);
    
  }
}

// If everything worked, then our test class has successfully:
// - created a linked Contact__c and Career_Path__c
// - set the Career Path's Job Title to 'oldTitle'
// - updated the Career Path to be Current, triggering your trigger
// - requeried for the update Contact
// - tested that the Contact's Job Title is now 'newTitle'

// There's some other points to make here, but I'll leave them out for now.
// Please comment/ message when you reach this point with the results of the test class.
// Feel free to tweak it as required, especially where the test records being created have required fields.