PlatinumItguru

@isTest
private class TestDeleteRestrictInvoice {
 
    // Invoice generator, with or without a Line Item
    static Invoice__c createNewInvoice(Boolean withLineItem) {
        // Create test Invoice and insert it into the database
        Invoice__c invoice = new Invoice__c();
        insert invoice;
 		       
        // The following is needed if you are following the tutorial

PlatinumItguru

@isTest
private class TestDeleteRestrictInvoice {

    // Invoice generator, with or without a Line Item
    static Invoice__c createNewInvoice(Boolean withLineItem) {
        // Create test Invoice and insert it into the database
        Invoice__c invoice = new Invoice__c();
        insert invoice;

        // Create test Line Item and insert it into the database, if withLineItem == true