@IsTest
public class ContainerReportTest{
static testMethod  void containerReportTest (){
   
    Container__c cont = new Container__c ( Name = 'CMLU', Provenance__c='OTHER', Statut__c='Open');
          insert cont;
    
     Articles_Containers__c ac = new Articles_Containers__c();
          Product2 p = new Product2(Name ='TestProduct'); 
          insert p;
    
                 
          ac.Product__c=p.ID;
          ac.Unit_Weight__c = 45; 
          ac.Unit_Cost__c = 87;
          ac.Container__c= cont.ID;
          ac.Number__c = 55;
          ac.UM__c ='UNIT(S)';    
          ac.Local_ID__c = 7888;
          ac.Comments__c = 'UNIT(S)';
          ac.Purpose__c='Consignment';
          ac.Condition__c= 'New';
           
           insert ac;
    Account acc = new Account(Name = 'TestACC', Representant__c='TestBene', Departement__c='Ouest', Address__c='102, Test');
    insert acc;
    
    Delivery__c del = new Delivery__c();
        del.Beneficiaire__c = acc.Id;
        del.Ration__c =3;
        del.Delivery_status__c='Pending';
        
        insert del;
    
    Item_Distributed__c itemDis = new Item_Distributed__c();
    itemDis.Quantity__c = 44;
    itemDis.Product__c = ac.Id;
    itemDis.Delivery__c =del.Id;
    
    insert itemDis;
    
    ContainerReportController CRC = new ContainerReportController();
    
}

}


The Controller is:


public class ContainerReportController
{
    public Container__c container {get;set;}
    public Map<String,List<Item_Distributed__c>> itemDistributed{get;set;}
    String containerId;
    
    
          
    
     
    public ContainerReportController()
    {
        container = new Container__c();
        itemDistributed = new Map<String,List<Item_Distributed__c>>();
        
        try
        {
            containerId = ApexPages.currentPage().getParameters().get('id');
            
            container = [SELECT Id,Name,DR__c, PO__c,Arrived_Date__c, Invoice__c, Pkl__c, Description__c, Container__c.Provenance__c, Percent_Distributed__c, Bill_of_Lading__c, Size_in_feet__c, Seal_No__c, 
                         (SELECT Id,Name,Prod__c,Number__c,Number_Distributed__c,Available__c,UM__c, Pending__c, Percentagedistributed__c FROM Articles_Containers__r)
                         FROM Container__c WHERE Id =:containerId];
            
            if(container != null)
            {
                Set<Id> articleContainersId = new Set<Id>();
                
                if(!container.Articles_Containers__r.isEmpty())
                {
                    for(Articles_Containers__c art :container.Articles_Containers__r)
                    {
                        articleContainersId.add(art.Id);
                        itemDistributed.put(art.Id, new List<Item_Distributed__c>());
                    }
                }
                
                List<Item_Distributed__c> lstItemDistributed = new List<Item_Distributed__c>();
                
                lstItemDistributed = [SELECT Id, Name,Product__c,Quantity__c,Delivery__c,Productt__c, Beneficiary__c, Date__c   
                                      FROM Item_Distributed__c WHERE  Del_Status__c='Delivered'AND Product__c IN :articleContainersId];
                
                if(!lstItemDistributed.isEmpty())
                {
                    for(Item_Distributed__c item :lstItemDistributed)
                    {
                        if(itemDistributed.containsKey(item.Product__c))
                        {
                            itemDistributed.get(item.Product__c).add(item);
                        }
                    }
                }
            }         
        }
        catch(Exception e)
        {
            System.debug(e.getMessage());
        }
    }
}