package.tests: Fix failure caused by wrong order of visit IDs

The in-mem/cass storage used to sort visits by (id, date). The last releases now sort by (date, id) like postgresql, but this test did not expect it.

This commit instantiate the loader after picking a date for the dummy visit, so the loader's visit always comes after the dummy one.

---

Migrated from D6164 (view on Phabricator)

swh/loader/package/tests/test_loader.py

@@ -169,14 +169,6 @@ def test_load_extids() -> None:
     rev4_swhid = CoreSWHID(object_type=ObjectType.REVISION, object_id=b"d" * 20)
     dir_swhid = CoreSWHID(object_type=ObjectType.DIRECTORY, object_id=b"e" * 20)
 
-    loader = StubPackageLoader(storage, "http://example.org")
-    patch.object(
-        loader,
-        "_load_revision",
-        return_value=(rev4_swhid.object_id, dir_swhid.object_id),
-        autospec=True,
-    ).start()
-
     # Results of a previous load
     storage.extid_add(
         [
@@ -215,6 +207,14 @@ def test_load_extids() -> None:
         ]
     )
 
+    loader = StubPackageLoader(storage, "http://example.org")
+    patch.object(
+        loader,
+        "_load_revision",
+        return_value=(rev4_swhid.object_id, dir_swhid.object_id),
+        autospec=True,
+    ).start()
+
     loader.load()
 
     assert loader._load_revision.mock_calls == [  # type: ignore