Handle Edge Cases

@isTest
static void newAccountWithNoDataReturnsZeroedSummary() {
    Account acc = new Account(Name = 'Brand New Account');
    insert acc;

    AccountHealthService service = new AccountHealthService();
    AccountHealthSummary summary = service.getHealthSummary(acc.Id);

    System.assertEquals(0, summary.openCaseCount);
    System.assertEquals(0, summary.averageResolutionDays);
    System.assertEquals(0, summary.totalWonRevenue);
}

1. @isTest — marks the test method.
2. static void newAccountWithNoDataReturnsZeroedSummary() { — the name states the scenario under test.
3. Account acc = new Account(Name = 'Brand New Account'); — deliberately no related Cases, Contacts, or revenue.
4. insert acc; — saves it, with nothing else inserted.
5. (blank line)
6. AccountHealthService service = new AccountHealthService(); — the class under test.
7. AccountHealthSummary summary = service.getHealthSummary(acc.Id); — calls the combining method against an Account with zero related data.
8. (blank line)
9. System.assertEquals(0, summary.openCaseCount); — confirms the zero-Case case.
10. System.assertEquals(0, summary.averageResolutionDays); — confirms the zero-closed-Case case.
11. System.assertEquals(0, summary.totalWonRevenue); — confirms the blank-revenue-field case.
12. } — closes the test method.

Every method built in Lesson 2 already handles empty results gracefully (if (closedCases.isEmpty()) { return 0; }) — this test formally confirms that design decision, exactly Module 17's habit of testing the empty/zero case explicitly rather than assuming it "probably works."

@AuraEnabled(cacheable=true)
public static AccountHealthSummary getAccountHealth(Id accountId) {
    if (accountId == null) {
        AuraHandledException ex = new AuraHandledException('An account must be selected to view health data.');
        ex.setMessage('An account must be selected to view health data.');
        throw ex;
    }
    return new AccountHealthService().getHealthSummary(accountId);
}

1. @AuraEnabled(cacheable=true) — unchanged from Lesson 4.
2. public static AccountHealthSummary getAccountHealth(Id accountId) { — the same controller method.
3. if (accountId == null) { — checked before calling the service at all.
4. AuraHandledException ex = new AuraHandledException('An account must be selected to view health data.'); — Module 34's exception type, constructed with a UI-safe message.
5. ex.setMessage('An account must be selected to view health data.'); — see the warning below.
6. throw ex; — throws it, ending the method here.
7. } — closes the if.
8. return new AccountHealthService().getHealthSummary(accountId); — unchanged, only reached with a non-null accountId.
9. } — closes the method.

This is Module 34's AuraHandledException lesson, applied to a genuinely real failure mode: an LWC could conceivably call this before a user has actually selected an Account — a clear, UI-safe message here is far better than whatever cryptic error a null Id would eventually cause deeper in the query logic.