Test data factory, the minimal version

@isTest
public class TestFactory {
    public static Account account() { return account('Acme ' + counter()); }

    public static Account account(String name) {
        return new Account(Name = name, Industry = 'Technology');
    }

    public static Contact contact(Id accountId) {
        return new Contact(FirstName = 'Test', LastName = 'Person ' + counter(),
                           AccountId = accountId,
                           Email = 'test' + counter() + '@example.com');
    }

    public static List<Account> accounts(Integer n) {
        List<Account> out = new List<Account>();
        for (Integer i = 0; i < n; i++) out.add(account());
        return out;
    }

    static Integer seq = 0;
    static Integer counter() { return ++seq; }
}

One class, builder-style defaults, no framework — the 80% of a test factory most orgs actually need.

Gotchas

Return unsaved records and let the test decide when to insert — tests that need Ids call insert themselves, tests that don't stay fast. The counter keeps unique fields unique across a 200-record build.