Mock CTO interview: the biggest risk when migrating from ASP to Django

# ======================================================================
# Q: CTO: "Tell me about the migration from ASP to Django. What was the biggest
# risk?"
#
# You: "The biggest risk was hidden business logic, for example B2B pricing
# rules written in stored procedures and in VBScript. I handled it with
# characterization tests: I recorded real scenarios from the old system
# (customer, SKU, quantity -> final price) and the new system had to produce
# exactly the same results. The second risk was the data: encodings
# (windows-1253), duplicates, orphaned records. I wrote an idempotent ETL with
# reconciliation reports. We did the cutover module by module behind nginx, with
# a rollback plan for every step."
# ======================================================================

# The cases were extracted from the legacy system (inputs + the price the ASP produced)
@pytest.mark.parametrize('case', load_cases('legacy_b2b_pricing.json'))
def test_b2b_price_matches_legacy(case):
    price = pricing.calculate(customer_id=case['customer'],
                              sku=case['sku'], qty=case['qty'])
    assert price == Decimal(case['legacy_price'])