Test the Feature

@isTest
private class CaseRoutingTest {
    @isTest
    static void caseWithAMatchingRuleRoutesToTheConfiguredQueue() {
        Test.startTest();
        Case c = new Case(Subject = 'Login broken', Priority = 'High', Type = 'Problem');
        insert c;
        Test.stopTest();

        Case saved = [SELECT Assigned_Queue__c FROM Case WHERE Id = :c.Id];
        System.assertNotEquals(null, saved.Assigned_Queue__c, 'Expected a matching High/Problem rule to assign a queue');
    }
}

1. @isTest — marks the test class.
2. private class CaseRoutingTest { — the class.
3. @isTest — marks the test method.
4. static void caseWithAMatchingRuleRoutesToTheConfiguredQueue() { — a clearly-named test.
5. Test.startTest(); — marks the start.
6. Case c = new Case(Subject = 'Login broken', Priority = 'High', Type = 'Problem'); — assuming a Case_Routing_Rule__mdt record exists for High/Problem.
7. insert c; — fires the trigger.
8. Test.stopTest(); — marks the end.
9. (blank line)
10. Case saved = [SELECT Assigned_Queue__c FROM Case WHERE Id = :c.Id]; — re-queries.
11. System.assertNotEquals(null, saved.Assigned_Queue__c, 'Expected a matching High/Problem rule to assign a queue'); — confirms the routing lookup actually matched and assigned the configured queue.
12. } — closes the test method.
13. } — closes the class.

@isTest
private class CaseRoutingTest {
    // ... caseWithAMatchingRuleRoutesToTheConfiguredQueue() from above ...

    @isTest
    static void caseWithNoMatchingRuleFallsBackToGeneralSupport() {
        Test.startTest();
        Case c = new Case(Subject = 'Unusual request', Priority = 'Low', Type = 'Feature Request');
        insert c;
        Test.stopTest();

        Case saved = [SELECT Assigned_Queue__c FROM Case WHERE Id = :c.Id];
        System.assertEquals('General Support', saved.Assigned_Queue__c, 'Expected the fallback queue when no rule matches');
    }
}

1. @isTest — marks the class.
2. private class CaseRoutingTest { — the same test class as before.
3. // ... caseWithAMatchingRuleRoutesToTheConfiguredQueue() from above ... — the first test method still lives here too.
4. (blank line)
5. @isTest — marks a second test method.
6. static void caseWithNoMatchingRuleFallsBackToGeneralSupport() { — a clearly-named test for the fallback.
7. Test.startTest(); — marks the start.
8. Case c = new Case(Subject = 'Unusual request', Priority = 'Low', Type = 'Feature Request'); — choosing a Priority/Type combination deliberately unlikely to have a configured rule.
9. insert c; — fires the trigger.
10. Test.stopTest(); — marks the end.
11. (blank line)
12. Case saved = [SELECT Assigned_Queue__c FROM Case WHERE Id = :c.Id]; — re-queries.
13. System.assertEquals('General Support', saved.Assigned_Queue__c, 'Expected the fallback queue when no rule matches'); — confirms Lesson 4's fallback logic actually fires.
14. } — closes the test method.
15. } — closes the class.

@isTest
private class CaseRoutingTest {
    // ... previous test methods ...

    @isTest
    static void bulkInsertWithMixedPriorityAndTypeRoutesEachCaseCorrectly() {
        List<Case> batch = new List<Case>{
            new Case(Subject = 'A', Priority = 'High', Type = 'Problem'),
            new Case(Subject = 'B', Priority = 'Low', Type = 'Question'),
            new Case(Subject = 'C', Priority = 'Medium', Type = 'Problem')
        };

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

        List<Case> saved = [SELECT Subject, Assigned_Queue__c FROM Case WHERE Id IN :batch];
        for (Case c : saved) {
            System.assertNotEquals(null, c.Assigned_Queue__c, 'Expected every Case in the batch to receive a queue assignment: ' + c.Subject);
        }
    }
}

1. @isTest — marks the class.
2. private class CaseRoutingTest { — the same test class.
3. // ... previous test methods ... — the earlier two tests still live here too.
4. (blank line)
5. @isTest — marks a third test method.
6. static void bulkInsertWithMixedPriorityAndTypeRoutesEachCaseCorrectly() { — a clearly-named test for the batch scenario.
7. List<Case> batch = new List<Case>{ — three Cases with different Priority/Type combinations.
8. new Case(Subject = 'A', Priority = 'High', Type = 'Problem'), — the first.
9. new Case(Subject = 'B', Priority = 'Low', Type = 'Question'), — the second.
10. new Case(Subject = 'C', Priority = 'Medium', Type = 'Problem') — the third.
11. }; — closes the list literal.
12. (blank line)
13. Test.startTest(); — marks the start.
14. insert batch; — inserts all three together.
15. Test.stopTest(); — marks the end.
16. (blank line)
17. List<Case> saved = [SELECT Subject, Assigned_Queue__c FROM Case WHERE Id IN :batch]; — re-queries all three.
18. for (Case c : saved) { — loops over the results.
19. System.assertNotEquals(null, c.Assigned_Queue__c, 'Expected every Case in the batch to receive a queue assignment: ' + c.Subject); — exactly Module 27's "test with multiple records" lesson, applied here — a single-record test could never confirm the bulkified lookup correctly handles several different combinations within the same batch.
20. } — closes the loop.
21. } — closes the test method.
22. } — closes the class.