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);
}

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);
}

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.