14.21Concurrent idempotency test

This is even stronger.

Send the same request:

10 times concurrently

Conceptually:

await Promise.all(
  Array.from({ length: 10 }, () =>
    createCustomer(request, sameCustomer)
  )
);

Then query Salesforce:

count = 1

This can reveal the Query→Create race we discussed in Module 12.