Add test assertion messages

Author: sebastianquek

tests/engines/constants.ts

@@ -0,0 +1,4 @@
+export const MSG_ASSERT_HAS_MULTIPLE_PAGES = "Only a single page was fetched";
+export const MSG_ASSERT_HAS_NON_FIRST_PAGE_RESULT =
+  "All results were from the first page";
+export const MSG_ASSERT_HAS_LAST_PAGE = "No last page was found";