Why do we have @TestSetup, when the result is as equal to not using them?

Question

If you create additional test records inside a test method, those records are rolled back at the end of the test method’s execution, which also happens when you’re not using test setup methods.

https://developer.salesforce.com/releases/release/Spring15/TestClasses

Answer 1

The scenario that @testSetup solves is simple.

Say you have a class that has three methods, all of which take a contact, and do different things. You might write a test for it like this:

@isTest public class ContactRejiggererTest {
    @isTest public static test_contact_rennovate() {
        Contact con = new Contact(FirstName='Al', LastName='Roker',Phone='612-555-1212');
        insert con;

        // query the contact for a Formula
        con = [SELECT FirstName,LastName,Favorite_Book_Formula__c FROM Contact LIMIT 1][0];
        System.assertEquals(null,Favorite_Book_Formula__c);
        ContactRejiggerer.rennovate(con);
        System.assertEquals('Building Bridges',Favorite_Book_Formula__c);
    }

    @isTest public static test_contact_mediate() {
        Contact con = new Contact(FirstName='Al', LastName='Roker',Phone='612-555-1212');
        insert con;

        // query the contact for a Formula
        con = [SELECT FirstName,LastName,Favorite_Book_Formula__c FROM Contact LIMIT 1][0];
        System.assertEquals(null,Favorite_Book_Formula__c);
        ContactRejiggerer.mediate(con);
        System.assertEquals('Zen and Motorcycles',Favorite_Book_Formula__c);
    }

    @isTest public static test_contact_deviate() {
        Contact con = new Contact(FirstName='Al', LastName='Roker',Phone='612-555-1212');
        insert con;

        // query the contact for a Formula
        con = [SELECT FirstName,LastName,Favorite_Book_Formula__c FROM Contact LIMIT 1][0];
        System.assertEquals(null,Favorite_Book_Formula__c);
        ContactRejiggerer.deviate(con);
        System.assertEquals('The Anarchist's Cookbook',Favorite_Book_Formula__c);
    }
}

There's a lot of code re-use here! We can solve that with a @testSetup!

@isTest public class ContactRejiggererTest {
   @testSetup public static createAl() {
        Contact con = new Contact(FirstName='Al', LastName='Roker',Phone='612-555-1212');
        insert con;
   }

    @isTest public static test_contact_rennovate() {
        con = [SELECT FirstName,LastName,Favorite_Book_Formula__c FROM Contact LIMIT 1][0];
        System.assertEquals(null,Favorite_Book_Formula__c);
        ContactRejiggerer.rennovate(con);
        System.assertEquals('Building Bridges',Favorite_Book_Formula__c);
    }

    @isTest public static test_contact_mediate() {
        con = [SELECT FirstName,LastName,Favorite_Book_Formula__c FROM Contact LIMIT 1][0];
        System.assertEquals(null,Favorite_Book_Formula__c);
        ContactRejiggerer.mediate(con);
        System.assertEquals('Zen and Motorcycles',Favorite_Book_Formula__c);
    }

    @isTest public static test_contact_deviate() {
        con = [SELECT FirstName,LastName,Favorite_Book_Formula__c FROM Contact LIMIT 1][0];
        System.assertEquals(null,Favorite_Book_Formula__c);
        ContactRejiggerer.deviate(con);
        System.assertEquals('The Anarchist's Cookbook',Favorite_Book_Formula__c);
    }
}

The contact gets rolled back to it's initial state after each test method.

Answer 2

There is also an undocumented limit to the total number of records that can be inserted when running unit tests. Moving to @TestSetup solved this problem for us in our most recent large project.