Test with Mocks

@isTest
public class PaymentGatewaySuccessMock implements HttpCalloutMock {
    public HttpResponse respond(HttpRequest request) {
        HttpResponse response = new HttpResponse();
        response.setStatusCode(200);
        response.setBody('{"transactionId": "txn_123"}');
        return response;
    }
}

@isTest
private class ProcessPaymentJobTest {
    @isTest
    static void successfulPaymentMarksOrderPaid() {
        Order__c order = new Order__c(Total__c = 500, Payment_Token__c = 'tok_abc');
        insert order;

        Test.setMock(HttpCalloutMock.class, new PaymentGatewaySuccessMock());

        Test.startTest();
        System.enqueueJob(new ProcessPaymentJob(order.Id, 500, 'tok_abc', 1));
        Test.stopTest(); // forces the Queueable job to actually run before this line returns

        Order__c updated = [SELECT Status__c, Payment_Reference__c FROM Order__c WHERE Id = :order.Id];
        System.assertEquals('Paid', updated.Status__c);
        System.assertEquals('txn_123', updated.Payment_Reference__c);
    }
}

Test.stopTest() (Module 31) does double duty here — it forces the Queueable job to run synchronously to completion, meaning the assertion afterward can safely check the result of the async work, not just that it was enqueued.

@isTest
public class PaymentGatewayDeclineMock implements HttpCalloutMock {
    public HttpResponse respond(HttpRequest request) {
        HttpResponse response = new HttpResponse();
        response.setStatusCode(402);
        response.setBody('{"reason": "Insufficient funds"}');
        return response;
    }
}

@isTest
static void declinedPaymentMarksOrderDeclined() {
    Order__c order = new Order__c(Total__c = 500, Payment_Token__c = 'tok_abc');
    insert order;

    Test.setMock(HttpCalloutMock.class, new PaymentGatewayDeclineMock());

    Test.startTest();
    System.enqueueJob(new ProcessPaymentJob(order.Id, 500, 'tok_abc', 1));
    Test.stopTest();

    Order__c updated = [SELECT Status__c, Decline_Reason__c FROM Order__c WHERE Id = :order.Id];
    System.assertEquals('Payment Declined', updated.Status__c);
    System.assertEquals('Insufficient funds', updated.Decline_Reason__c);
}

This confirms 402 gets routed correctly through Lesson 2's status-code branching all the way to the final Order__c status — the full chain, exercised end to end.

@isTest
public class PaymentGatewayErrorMock implements HttpCalloutMock {
    public HttpResponse respond(HttpRequest request) {
        HttpResponse response = new HttpResponse();
        response.setStatusCode(500);
        return response;
    }
}

@isTest
static void thirdFailedAttemptGivesUpWithPaymentError() {
    Order__c order = new Order__c(Total__c = 500, Payment_Token__c = 'tok_abc');
    insert order;

    Test.setMock(HttpCalloutMock.class, new PaymentGatewayErrorMock());

    Test.startTest();
    System.enqueueJob(new ProcessPaymentJob(order.Id, 500, 'tok_abc', 3)); // already the 3rd attempt
    Test.stopTest();

    Order__c updated = [SELECT Status__c FROM Order__c WHERE Id = :order.Id];
    System.assertEquals('Payment Error', updated.Status__c);
}

Starting at attemptNumber = 3 (the limit) directly, rather than simulating all three attempts, tests Lesson 4's boundary condition precisely — confirming the job gives up and records Payment Error instead of chaining a fourth attempt.