In order to avoid cementing an API before implementation but also stick with the "everything-starts-with-a-test" approach (which I appreaciate its benefits), I like to break down my code into smaller functions, each with the simplest possible API.

For example, fetch_url($urlstr), html2dom($htmlstr), extract_urls_from_dom($dom), is_url_pointing_to_pdf($urlstr). And I leave the user-calling function las. Until I reach the time to implement it, I am already testing these simple functions and the final user-calling function's API is crystallising in my head.

So, I start with a test! But for the bricks so-to-speak of the app. And in doing so, I slowly slowly settle on where to place the loo.

p.s. SaNkoR's Refactor your code so you can call and test the 'logic' without grabbing a remote page. is good: use locally-fetched html to test your code rather than hitting the sites with the risk of your tests failing each time they change. On this, I put network-access tests in author tests, or live tests which are only executed by me and not by the potential user.

bw, bliako