I am new to test classes. My Test class is giving only 36% coverage.What else i  can check in my test class

Test class:

@isTest
public class ITOVC_TargetMasterGovernanceClassTest {
    @TestSetup
    static void setup(){
        ITOVC_Target__c target1 = new ITOVC_Target__c(Name='TG01',Start_Date__c=Datetime.newInstance(2018, 01, 01), End_Date__c=Datetime.newInstance(2018, 01, 31),Target_Value__c=1);
        insert target1;
    }
  @isTest  static void testDuplicateRecordsForSameStartEndDate(){
        ITOVC_Target__c target2 = new ITOVC_Target__c(Name='TG01',Start_Date__c=Datetime.newInstance(2018, 01, 01), End_Date__c=Datetime.newInstance(2018, 01, 31),Target_Value__c=1);
        try {
           insert target2;
       } catch (Exception e) { 
           System.debug('An error happened, as predicted!');
       }
    }
}
apex class:

public class ITOVC_TargetMasterGovernanceClass {
    public void DuplicateRecordsForSameStartEndDate(List<ITOVC_Target__c> newTgId){
        List<ITOVC_Target__c> TgList = ([Select Name,Target_Value__c,Start_date__c,End_date__c from ITOVC_Target__c limit 10000]);
        for(ITOVC_Target__c tg : TgList){
            system.debug('ITOVC_Target__c tg :  ' + tg);
            for(ITOVC_Target__c newTg : newTgId ){
                system.debug('ITOVC_Target__c newtg :  ' + newtg);
                if(tg.Start_Date__c !=Null || tg.End_Date__c !=Null){
                    if( 
                        ((newTg.End_Date__c >= tg.Start_Date__c && newTg.End_Date__c <= tg.End_Date__c) ||
                        (newTg.Start_Date__c >= tg.Start_Date__c && newTg.End_Date__c <= tg.End_Date__c)||
                        (newTg.Start_Date__c >= tg.Start_Date__c && newTg.Start_Date__c <= tg.End_Date__c)||
                        (newTg.Start_Date__c < tg.Start_Date__c && newTg.End_Date__c > tg.End_Date__c))&&
                        (newTg.Name >= tg.Name)&&
                              (newTg.Target_Value__c >= tg.Target_Value__c)
                      ){

                              newTg.addError('Start date and End date are getting overlapped with existing records.');

                       }
                 }
            }
     }
    }
    public void recordsCantBeDeleted(List<ITOVC_Target__c> oldTgId){

        for(ITOVC_Target__c TgDel : oldTgId){

            TgDel.addError('You can\'t delete master target record');
        }
    }
}
apex trigger:

trigger ITOVC_TargetMasterGovernanceTrigger on ITOVC_Target__c (before insert,before update, before delete) {
     ITOVC_TargetMasterGovernanceClass thClass = new ITOVC_TargetMasterGovernanceClass();
    if(trigger.isInsert || Trigger.isUpdate){
        system.debug('Trigger.new contains :   '+Trigger.new);
        thClass.DuplicateRecordsForSameStartEndDate(Trigger.new);
    }
   if(Trigger.isDelete)
    {
        thClass.recordsCantBeDeleted(Trigger.old);
        system.debug('Trigger.old contains :   '+Trigger.old);
    }

}