Trigger :

trigger AccountUpdateTrigger on Invoice__c (after insert) {
    Set<String> customerLeadon = new Set<String>();
    Set<Id> accountId = new Set<Id>();
    Map<Id,String> invoiceMap = new Map<Id,String>();
    Map<String,Id> accountMap = new Map<String,Id>();
    Map<Id,String> accountNameMap = new Map<Id,String>();
    List<Invoice__c> invoiceUpd = new List<Invoice__c>();
    if(Trigger.isAfter && Trigger.isInsert && RecursiveStopping.isRecursive == True){
        RecursiveStopping.isRecursive = false;
        for(Invoice__c inv:Trigger.new){
            if(inv.AccountNumber__c.contains('12868') && inv.LeadOn__c.contains('000')){
                accountId.add(inv.Account__c);
                
              }
          }
        System.debug('ACCId=='+accountId);
        if(accountId.size()>0){
            for(Account acc:[SELECT Id,Name FROM Account WHERE Id IN:accountId]){
                accountNameMap.put(acc.Id,acc.Name);
            }
            for(Invoice__c inv:Trigger.new){
                System.debug('Acc='+inv.Account__c);
                String accName = accountNameMap.get(inv.Account__c);
                if(accName.contains('Echuca Camera House') && inv.AccountNumber__c.contains('12868') && inv.LeadOn__c.contains('000')){
                    customerLeadon.add(inv.AccountNumber__c+'   '+inv.LeadOn__c);
                    invoiceMap.put(inv.Id,inv.AccountNumber__c+'   '+inv.LeadOn__c);
                }
            }
            System.debug('CUST=='+customerLeadon);
            
            if(customerLeadon.size()>0){
                for(Account acc:[SELECT Id,Name,Customer_Account_and_Lead_On__c FROM Account WHERE Customer_Account_and_Lead_On__c IN: customerLeadon]){
                    accountMap.put(acc.Customer_Account_and_Lead_On__c,acc.Id);
                } 
            }
            if(accountMap.size()>0){
                for(Invoice__c inv:Trigger.new){
                    Invoice__c invUpd = new Invoice__c();
                    invUpd.Id = inv.Id ;
                    if(accountMap.get(invoiceMap.get(inv.Id)) != null){
                        invUpd.Account__c = accountMap.get(invoiceMap.get(inv.Id));
                    }
                    invoiceUpd.add(invUpd);
                }
                update invoiceUpd;
            }
        }
    }
}




My Test Class:


@istest
public class AccountUpdateTriggerTest {
    
    @istest
    public static void testData(){
       Account acc = new Account();
       acc.Name = 'Raleru Account';
       acc.Shipping_Address_Maps_To__c = '12868   000';
       acc.Customer_Account_and_Lead_On__c = '12868   000';
       insert acc;
       
       Account acc1 = new Account();
       acc1.Name = 'Echuca Camera House';
       acc1.Shipping_Address_Maps_To__c = '12868   600';
       acc1.Customer_Account_and_Lead_On__c = '12868   600';
       insert acc1;
        
      System.debug('ACC=='+acc);
      System.debug('Acc1=='+acc1);
        
      Invoice__c inv  = new Invoice__c();
      inv.Name = '332456';
      inv.InvoiceNumber__c = '332456';
      inv.Account__c = acc1.Id;
      inv.AccountNumber__c = '12868';
      inv.LeadOn__c = '000';
      insert inv;
      System.debug('CUST SQL='+[SELECT Id,Name,Customer_Account_and_Lead_On__c FROM Account WHERE Customer_Account_and_Lead_On__c =: '12868   000']);  
      
    }
    
}