fix: Allow union of destinations in fulfillment tests

.cspell/custom-words.txt

@@ -21,6 +21,7 @@ Commerce
 credentialization
 credentialless
 Credentialless
+cust
 datamodel
 Depot
 dpan
@@ -44,6 +45,7 @@ linenums
 llmstxt
 Lowe's
 Macy's
+Malform
 mastercard
 Mastercard
 mkdocs
@@ -70,15 +72,19 @@ shellcheck
 Shopee
 shopify
 Shopify
+Smallville
 Stripe
 superfences
 Target
 UCP
 Ulta
+Villagetown
 Visa
 vulnz
 Wayfair
 Worldpay
+wumpus
+Wumpus
 yaml
 yml
 Zalando

fulfillment_test.py

@@ -413,16 +413,10 @@ def test_known_customer_new_address(self) -> None:
     method = updated_checkout.model_extra["fulfillment"]["methods"][0]
 
     # Should see the new address (and potentially the injected ones if the
-    # server merges them, but based on current implementation logic, client
-    # payload overrides/merges depending on how Pydantic handles lists.
-    # The server logic appends if missing. If we provide it, it might not
-    # inject. Let's verify behavior. The server logic says:
-    # if m_data["type"] == "shipping" and ("destinations" not in m_data
-    # or not m_data["destinations"]): inject...
-    # So if we provide destinations, it WON'T inject.
-
-    self.assertLen(method["destinations"], 1)
-    self.assertEqual(method["destinations"][0]["id"], "dest_new")
+    # server merges them). The server returns a union of known + provided.
+    self.assertGreaterEqual(len(method["destinations"]), 1)
+    dest_ids = [d["id"] for d in method["destinations"]]
+    self.assertIn("dest_new", dest_ids)
 
     # And we should get options calculated for CA
     group = method["groups"][0]
@@ -470,10 +464,11 @@ def test_known_user_existing_address_reuse(self) -> None:
 
     method = updated_checkout.model_extra["fulfillment"]["methods"][0]
     self.assertIsNotNone(method["destinations"])
-    self.assertLen(method["destinations"], 1)
+    self.assertGreaterEqual(len(method["destinations"]), 1)
 
     # Should reuse addr_1
-    self.assertEqual(method["destinations"][0]["id"], "addr_1")
+    dest_ids = [d["id"] for d in method["destinations"]]
+    self.assertIn("addr_1", dest_ids)
 
   def test_free_shipping_on_expensive_order(self) -> None:
     """Test that free shipping is offered for orders over $100."""