System.ListException: List index out of bounds: 0 when list is not empty

Question

I have an apex code like that :

List<Campaign> campaigns = DataFactory.createCampaign();

    Contact contact = new Contact(/*some fields here*/);
    if(!campaigns.isEmpty()){
        DataFactory.createCampaignMember(campaigns[0], contact);
    }

If I put a system.debug(campaings) I retrieve 3 campaings, so my list campaigns is not empty. But when I run the code (it is in an apex test class) I got this error :

System.ListException: List index out of bounds: 0

at the line DataFactory.createCampaignMember(campaigns[0], contact);

How can I resolve this error ?

EDIT :

Here is the method of the DataFactory :

public static CampaignMember createCampaignMember(Campaign campaign, Contact contact){
  List<Contact> idContact = [SELECT Id FROM Contact WHERE FirstName=:contact.FirstName LIMIT 1];
  List<Campaign> idCampaign = [SELECT Id FROM Campaign WHERE Name=:campaign.Name LIMIT 1];
  CampaignMember campaignMember = new CampaignMember(ContactId=idContact.get(0).Id, CampaignId=idCampaign.get(0).Id);
  return campaignMember;
}

The error is indicated on the line CampaignMember(ContactId=idContact.get(0).Id, CampaignId=idCampaign.get(0).Id);

Answer 1

in your createCampaignMember method you have List<Contact> idContact = [SELECT Id FROM Contact WHERE FirstName=:contact.FirstName LIMIT 1]; soql that queries Contact.

but from test class you don't insert such contact Contact contact = new Contact(/*some fields here*/); you need to insert this contact.

List<Campaign> campaigns = DataFactory.createCampaign();

Contact cont = new Contact(/*some fields here*/);
insert cont;
if(!campaigns.isEmpty()){
    DataFactory.createCampaignMember(campaigns[0], cont);
}

make sure that List<Campaign> campaigns = DataFactory.createCampaign(); also inserts campaigns to DB