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[!IMPORTANT] Every fixture, rulebook, and calculator output in this lab is synthetic and non-binding. Nothing here represents an actual Desjardins product, rate, or policy, and no regulator or insurer has reviewed or endorsed this material.

Overview

Item	Value
Duration	40 minutes
Level	Intermediate
Prerequisites	Lab 01

Learning Objectives

By the end of this lab, you will be able to:

• Describe the ApprovalRepository state machine: DRAFT, PENDING_REVIEW, APPROVED, REJECTED
• Explain why the reviewer of a case can never be the same person who prepared it
• Trigger and catch a SelfApprovalError yourself
• Confirm that revising a decided case resets it to DRAFT and clears the prior decision

Exercises

Exercise 3.1: Read the State Machine

Open apps/workshop/approval_repository.py and read the module docstring and the ApprovalRepository class. Identify:

• create_draft creates a case in DRAFT at revision 1
• submit_for_review moves DRAFT to PENDING_REVIEW
• approve and reject both call the private _decide method, which moves PENDING_REVIEW to APPROVED or REJECTED
• revise creates a new revision from any state, resetting it to DRAFT and clearing the reviewer and approval timestamp

Exercise 3.2: Run the Existing Tests

python -m pytest apps/workshop/tests/test_approval_repository.py -v

Expected result: every test passes, covering the full state machine and revision-invalidation behavior.

Exercise 3.3 (Hands-on): Trigger a Self-Approval Rejection

In a Python shell, create a draft with a preparer, submit it for review, then attempt to approve it with that same preparer as the reviewer.

python -c "
import sys
sys.path.insert(0, 'apps/workshop')
from approval_repository import ApprovalRepository, SelfApprovalError

repo = ApprovalRepository()
repo.create_draft('CASE-LAB-001', preparer_id='EMP-001')
repo.submit_for_review('CASE-LAB-001', actor_id='EMP-001')

try:
    repo.approve('CASE-LAB-001', reviewer_id='EMP-001')
    print('UNEXPECTED: self-approval succeeded')
except SelfApprovalError as exc:
    print(f'Blocked as expected: {exc}')

record = repo.approve('CASE-LAB-001', reviewer_id='EMP-002')
print(f'Approved by a distinct reviewer: state={record.state}')
"

Expected result: the first approve call raises SelfApprovalError. The second call, with a different reviewer_id, succeeds and reports state=APPROVED.

Exercise 3.4 (Hands-on): Revise an Approved Case

Continuing in the same shell session, call repo.revise('CASE-LAB-001', actor_id='EMP-001') and inspect the returned record.

Expected result: state is back to DRAFT, revision has incremented, and reviewer_id/approved_at are cleared. The prior approval no longer applies to the new revision.

Validation Checklist

• pytest apps/workshop/tests/test_approval_repository.py -v passes
• You triggered and caught SelfApprovalError from a reviewer_id equal to the case’s preparer_id
• A distinct reviewer_id approved the same case successfully
• revise after APPROVED reset the case to DRAFT and cleared the reviewer and approval timestamp

Knowledge Check

• Why does _decide check reviewer_id == record.preparer_id before it checks the case’s current state?
• What happens if you call approve twice in a row with the same reviewer_id on an already-approved case? Read _decide again if you are unsure.

Next Steps

Continue to Lab 04: The Application MCP Server.