How Can You Test an API’s Pagination?
From the earlier reference collection. Read the current software blog.
Use a deterministic dataset to verify page order, complete coverage, and uniqueness across page boundaries.
Create a dataset that crosses pages
A pagination test needs more records than fit on one page. Configure a small page size, such as three, and provide seven records with stable identifiers. The expected pages should cover the ordered sequence in chunks, including a final partial page. This setup exposes off-by-one errors that a one-page fixture cannot reveal.
Choose a deterministic sort key and state whether ordering is ascending or descending. If the API promises stable ordering, include records with equal primary sort values and define the tie-breaker, such as identifier. Without a tie-breaker, a test may mistake legitimate nondeterminism for a pagination defect.
Check coverage and duplicates
Fetch every page and concatenate the results. Assert that the combined identifiers equal the complete expected sequence, not merely that the total count matches. A duplicate and a missing record can cancel out numerically, so also assert uniqueness and set equality.
Inspect the boundaries: the last record on page one should be followed by the next expected record on page two. Test the first page, a middle page, the final partial page, and the page after the end. The API should return its documented empty or terminal response for that last request.
Exercise the continuation mechanism
If clients use offsets, verify that the next offset advances by the number of records returned or by the documented page size. If the API uses a cursor, pass each returned cursor unchanged and confirm that the sequence terminates. Do not assume that a cursor is a numeric page number; treat its format as opaque unless the API contract says otherwise.
Also check metadata such as next-page links, total counts, and continuation tokens when they are part of the response contract. A correct record list with a broken continuation link can still strand clients before they reach the end.
Test consistency assumptions
If records can change while pages are being fetched, document whether the API promises a snapshot or only best-effort traversal. A static fixture tests the pagination algorithm; separate tests can cover updates during traversal if the contract defines their behavior.
A good pagination suite explains the ordering and termination rules, then proves that a consumer can walk the entire result once. Failure output should identify the page and unexpected identifiers so boundary defects are easy to locate.