I'm trying to write a test class and load bunch of test lead's data but for some reason when I call the static resource (that has my CSV) is not recognizing the custom fields. Example, Lead_insurance_Id__c

My CSV file - static resource:

// Example of how my CSV looks like

Id, Firstname, Lastname, Leads_Insurance_ID__c,..etc

000012, Fares, Alsyoufi, 12184111, ..etc
000011, Fare,syoufi, 12184211, ..etc
000013, Fares, syouf, 12184311, ..etc

My test class:
 

@isTest 
global class DataUtil {
    static testmethod void testLoadData() {
        // Load the test accounts from the static resource
        List<sObject> ls = Test.loadData(Account.sObjectType, 'TestData');
        
       }
}

Error message: 



Seems like the standard Salesforce fields didn't cause any execptions but custom fields did (I tried other one beside Lead_Insurance_Id__c) and I still got the same error message. 

P.S:
I've tried to change my CSV header to all of these formats but non helped:

LEADS_INSURANCE_ID__c
Leads_insurance_Id__c
Lead.DLeads_insurance_Id__c
Insurance ID (Field's label)