API Collection Runner: Bruno Run, Diff and Fix Loop

Real output from a demo shop API with a planted tax bug, run with bru 3.3.0.

Summary

One request failed. cart/Cart total charged tax on the full subtotal instead of the subtotal after the coupon. I fixed pricing.py and restarted the server. The whole collection now passes, 7 of 7 requests and 17 of 17 checks.

First run

Shop API  env local  engine bru 3.3.0 (--engine bru)  run 20261016-132604

  #  RESULT  REQUEST                STATUS  CHECKS  DIFF
  1  PASS    health/Health          200     2/2     same
  2  PASS    auth/Login             200     2/2     same
  3  PASS    catalog/List products  200     3/3     same
  4  PASS    cart/Create cart       201     2/2     same
  5  PASS    cart/Add item          201     2/2     same
  6  FAIL    cart/Cart total        200     3/5     2 changes
  7  PASS    cart/Delete cart       204     1/1     same

FAIL  cart/Cart total
  assert  res.body.taxCents: eq {{expected_tax}}  expected 330 to equal 297
  assert  res.body.totalCents: eq {{expected_total}}  expected 3928 to equal 3895
  diff vs baseline (approved in run 20261016-132601) (masked: server, date, x-request-id)
    $.taxCents    297 -> 330
    $.totalCents  3895 -> 3928
  request  GET http://127.0.0.1:7878/carts/d571dc97-98a4-4fd4-a65e-3f26b04c04f6/total?coupon=SAVE10

6 passed, 1 failed  (checks 15/17)
exit 1 (FAILED)

Cause

The cart holds two Field caps, a 3998 cent subtotal. SAVE10 takes 400 off. Tax at 8.25% belongs on the 3598 that is left, which is 297. The server taxed the full 3998 and got 330, so the total came out 33 cents high. quote() in pricing.py computed tax from subtotal instead of subtotal - discount.

Fix

     discount = cents(subtotal * rate)
-    tax = cents(subtotal * TAX_RATE)
+    taxable = subtotal - discount
+    tax = cents(taxable * TAX_RATE)
     return {
         "subtotalCents": subtotal,
         "discountCents": discount,
         "taxCents": tax,
-        "totalCents": subtotal - discount + tax,
+        "totalCents": taxable + tax,

Proof

I stopped the process on port 7878, started the server again and waited for /health. Then I reran only the failure. The tool added the login and cart setup it depends on.

rerun: 1 failing key(s) from run 20261016-132604, plus setup

  #  RESULT  REQUEST          STATUS  CHECKS  DIFF
  1  PASS    cart/Cart total  200     5/5     same
setup: 3 steps PASS (auth/Login provides {{token}}; cart/Create cart, cart/Add item run earlier in cart/)

4 passed  (checks 11/11)
exit 0 (OK)

Then the whole collection.

  #  RESULT  REQUEST                STATUS  CHECKS  DIFF
  1  PASS    health/Health          200     2/2     same
  2  PASS    auth/Login             200     2/2     same
  3  PASS    catalog/List products  200     3/3     same
  4  PASS    cart/Create cart       201     2/2     same
  5  PASS    cart/Add item          201     2/2     same
  6  PASS    cart/Cart total        200     5/5     same
  7  PASS    cart/Delete cart       204     1/1     same

7 passed  (checks 17/17)
exit 0 (OK)

Next steps

• Review the change to pricing.py and commit it.
• No baseline changed. Every response matches the approved one again, so .acr/baselines/ has nothing to commit.
• I did not touch the staging env. It would send POST and DELETE to staging.shop.example, so the tool will stop and I will ask you first.