Test Data Factories

@isTest
static void test1() {
    Account acc = new Account(Name = 'Test Account', Industry = 'Technology');
    insert acc;
    // ...
}

@isTest
static void test2() {
    Account acc = new Account(Name = 'Test Account', Industry = 'Technology');
    insert acc;
    // ...
}

1. @isTest — marks the first test method.
2. static void test1() { — one test.
3. Account acc = new Account(Name = 'Test Account', Industry = 'Technology'); — every test method needing a valid Account repeats the exact same setup.
4. insert acc; — saves it.
5. // ... — the rest of this test.
6. } — closes this test method.
7. (blank line)
8. @isTest — marks a second test method.
9. static void test2() { — a different test.
10. Account acc = new Account(Name = 'Test Account', Industry = 'Technology'); — the exact same setup, duplicated.
11. insert acc; — saves it.
12. // ... — the rest of this test.
13. } — closes this test method — the same duplication problem Modules 12, 17, 22, and 23 each closed out by extracting a shared private method, now showing up in test code specifically.

@isTest
private class AccountRollupServiceTest {
    private static Account createTestAccount() {
        Account acc = new Account(Name = 'Test Account', Industry = 'Technology');
        insert acc;
        return acc;
    }

    @isTest
    static void test1() {
        Account acc = createTestAccount();
        // ...
    }

    @isTest
    static void test2() {
        Account acc = createTestAccount();
        // ...
    }
}

1. @isTest — marks the class.
2. private class AccountRollupServiceTest { — the class.
3. private static Account createTestAccount() { — private static — callable directly from any @isTest static method in the same class, exactly like the trigger handler's private helpers from Module 22.
4. Account acc = new Account(Name = 'Test Account', Industry = 'Technology'); — the one, now-shared setup.
5. insert acc; — saves it.
6. return acc; — hands it back.
7. } — closes the factory method.
8. (blank line)
9. @isTest — marks the first test.
10. static void test1() { — a test.
11. Account acc = createTestAccount(); — delegates instead of repeating the setup.
12. // ... — the rest of this test.
13. } — closes this test.
14. (blank line)
15. @isTest — marks the second test.
16. static void test2() { — a different test.
17. Account acc = createTestAccount(); — the same shared factory.
18. // ... — the rest of this test.
19. } — closes this test.
20. } — closes the class.

Any future change to what a "valid test Account" needs happens in exactly one place.

@isTest
public class TestDataFactory {
    public static Account createAccount(String name) {
        Account acc = new Account(Name = name, Industry = 'Technology');
        insert acc;
        return acc;
    }

    public static Book__c createBook(String title) {
        return new Book__c(Title__c = title, ISBN__c = '000-0-000-00000-0', Is_Checked_Out__c = false);
    }
}

// used from any test class:
Account acc = TestDataFactory.createAccount('Riverbend Farms');

1. @isTest — marks the class as test-only, but public so it can be called from other test classes.
2. public class TestDataFactory { — for data patterns reused across multiple test classes, not just within one.
3. public static Account createAccount(String name) { — a reusable factory method.
4. Account acc = new Account(Name = name, Industry = 'Technology'); — builds it.
5. insert acc; — saves it.
6. return acc; — hands it back.
7. } — closes the method.
8. (blank line)
9. public static Book__c createBook(String title) { — a second factory method, for a different object.
10. return new Book__c(Title__c = title, ISBN__c = '000-0-000-00000-0', Is_Checked_Out__c = false); — builds and returns it directly.
11. } — closes the method.
12. } — closes the class.
13. (blank line)
14. // used from any test class: — the label for the usage example.
15. Account acc = TestDataFactory.createAccount('Riverbend Farms'); — avoids duplicating the same setup logic across every test file in the org — the natural next step once a single class's private helper isn't enough.