INVALID_FIELD_FOR_INSERT_UPDATE, cannot specify Id in an insert call: [Id] Error When Running Test Class

Question

I've been trying to run my test class via Visual Studio Code, but I get the following error message:

INVALID_FIELD_FOR_INSERT_UPDATE, cannot specify Id in an insert call: [Id]

Deployment to org is successful though, but it keeps displaying such message when I run it.

As for the controller, it just inserts a new custom object record.

Meanwhile, following are both controller, TestDataFactory, test class I've been working on:

CustObj1Controller

public with sharing class CustObj1Controller {
    
    @AuraEnabled
    public static CustObj1__c createCustomObj1(CustObj1__c newCustObj1){
        insert newCustObj1;
        return newCustObj1;    
    }
   
}

TestDataFactory

@isTest
public with sharing class TestDataFactory {
    public static List<CustObj1__c> createCustObj1(Integer count, Boolean performDML) {
        List<CustObj1__c> custObj1List = new List<CustObj1__c>();
        for(Integer i=0; i < count; i++) {
            CustObj1__c custObj1 = new CustObj1__c();
            custObj1.Field1__c = 'this is a sample field value' + i;
            custObj1List.add(custObj1);
        }    
        if(performDML) {
            insert custObj1List;
        }
        return custObj1List;
    }
}

CustObj1ControllerTest

@isTest
private class CustObj1ControllerTest {
    @TestSetup
    static void testSetup(){
        Test.startTest();
        List<CustObj1__c> custObj1List = TestDataFactory.createCustObj1(1, false);    
        CustObj2__c custObj2 = new CustObj2__c();
        custObj2.CustObj1__c = custObj1List[0].Id;
        custObj2.Field1__c = 'Field1';
        custObj2.Field2__c = 'Field2'; 
        insert custObj2; 
        Test.stopTest();
    }
    @isTest static void testCustObj1() {
        List<CustObj2__c> custObj2List  =  [SELECT CustObj1__c FROM CustObj2__c];
        System.assertEquals(true,custObj2List.size()>0);
        CustObj1Controller.createCustomObj1(custObj2List[0]);
    }
}

Hoping someone could help me on this.

Answer 1

The records are already inserted (the true parameter causes the method to insert the records). Either use false, so you can add additional fields before inserting, or use the update method to update the records.