Build a Bulk-Safe Trigger

public class LoanApplicationTriggerHandler {
    private static final Integer LOAN_TERM_MONTHS = 60;

    public void beforeInsert(List<Loan_Application__c> newApplications) {
        LoanValidationService validator = new LoanValidationService();
        LoanCalculationService calculator = new LoanCalculationService();

        for (Loan_Application__c app : newApplications) {
            validator.validate(app.Requested_Amount__c, app.Annual_Income__c, app.Credit_Score__c);

            Decimal rate = calculator.calculateInterestRate(app.Credit_Score__c);
            app.Interest_Rate__c = rate;
            app.Monthly_Payment__c = calculator.calculateMonthlyPayment(app.Requested_Amount__c, rate, LOAN_TERM_MONTHS);
            app.Status__c = determineStatus(app.Credit_Score__c, app.Requested_Amount__c, app.Annual_Income__c);
        }
    }

    private String determineStatus(Decimal creditScore, Decimal amount, Decimal income) {
        if (creditScore >= 700 && amount <= income * 0.4) {
            return 'Pre-Approved';
        } else if (creditScore >= 600) {
            return 'Manual Review';
        } else {
            return 'Declined';
        }
    }
}

1. public class LoanApplicationTriggerHandler { — a genuinely realistic trigger handler.
2. private static final Integer LOAN_TERM_MONTHS = 60; — a shared constant.
3. (blank line)
4. public void beforeInsert(List<Loan_Application__c> newApplications) { — the entry point.
5. LoanValidationService validator = new LoanValidationService(); — validation (Lesson 3).
6. LoanCalculationService calculator = new LoanCalculationService(); — calculation (Lesson 2).
7. (blank line)
8. for (Loan_Application__c app : newApplications) { — loops over the new applications, entirely in memory.
9. validator.validate(app.Requested_Amount__c, app.Annual_Income__c, app.Credit_Score__c); — validates first — throws if invalid.
10. (blank line)
11. Decimal rate = calculator.calculateInterestRate(app.Credit_Score__c); — computes the rate.
12. app.Interest_Rate__c = rate; — stores it.
13. app.Monthly_Payment__c = calculator.calculateMonthlyPayment(app.Requested_Amount__c, rate, LOAN_TERM_MONTHS); — computes and stores the payment.
14. app.Status__c = determineStatus(app.Credit_Score__c, app.Requested_Amount__c, app.Annual_Income__c); — the approval decision (Lesson 1's policy, finally implemented).
15. } — closes the loop — no SOQL or DML inside it at all.
16. } — closes the method.
17. (blank line)
18. private String determineStatus(Decimal creditScore, Decimal amount, Decimal income) { — the policy, as code.
19. if (creditScore >= 700 && amount <= income * 0.4) { — the pre-approval rule.
20. return 'Pre-Approved'; — its outcome.
21. } else if (creditScore >= 600) { — the manual-review rule.
22. return 'Manual Review'; — its outcome.
23. } else { — everything else.
24. return 'Declined'; — the decline outcome.
25. } — closes the if/else if/else.
26. } — closes the method.
27. } — closes the class.

@isTest
private class LoanApplicationTriggerHandlerTest {
    @isTest
    static void bulkApplicationsAllProcessCorrectly() {
        List<Loan_Application__c> applications = new List<Loan_Application__c>();
        for (Integer i = 0; i < 200; i++) {
            applications.add(new Loan_Application__c(
                Requested_Amount__c = 10000, Annual_Income__c = 50000, Credit_Score__c = 720
            ));
        }

        Test.startTest();
        insert applications;
        Test.stopTest();

        List<Loan_Application__c> saved = [SELECT Status__c, Interest_Rate__c FROM Loan_Application__c];
        System.assertEquals(200, saved.size());
        for (Loan_Application__c app : saved) {
            System.assertEquals('Pre-Approved', app.Status__c);
            System.assertEquals(6.5, app.Interest_Rate__c);
        }
    }
}

1. @isTest — marks the class.
2. private class LoanApplicationTriggerHandlerTest { — this is Module 31's "Testing Triggers: Bulk and Edge Cases" lesson, applied the moment the trigger exists.
3. @isTest — marks the test method.
4. static void bulkApplicationsAllProcessCorrectly() { — the test.
5. List<Loan_Application__c> applications = new List<Loan_Application__c>(); — 200 applications to build.
6. for (Integer i = 0; i < 200; i++) { — loops 200 times.
7. applications.add(new Loan_Application__c( — builds one application.
8. Requested_Amount__c = 10000, Annual_Income__c = 50000, Credit_Score__c = 720 — values that should all qualify for pre-approval.
9. )); — closes the constructor call and add().
10. } — closes the loop.
11. (blank line)
12. Test.startTest(); — marks the boundary.
13. insert applications; — one insert, 200 records.
14. Test.stopTest(); — marks the end.
15. (blank line)
16. List<Loan_Application__c> saved = [SELECT Status__c, Interest_Rate__c FROM Loan_Application__c]; — re-queries all 200.
17. System.assertEquals(200, saved.size()); — confirms all were saved.
18. for (Loan_Application__c app : saved) { — loops over the results.
19. System.assertEquals('Pre-Approved', app.Status__c); — confirms every single one processed correctly.
20. System.assertEquals(6.5, app.Interest_Rate__c); — and got the right rate.
21. } — closes the loop.
22. } — closes the test method.
23. } — closes the class.