At the moment there’s no sandbox or equivalent, you’re correct that pledging to yourself on the live site is the most popular approach at this time. There’s been some mention by the Patreon team of someday adding a sandbox, you can find the most recent mention of that here:
Here’s a citation from the documentation on the current approach: API Reference
Testing of the API can be done by creating dummy accounts through the website. To test pledging, it can be useful to:
- Create a Patreon account with creator page and set it to “per post”.
- Create another Patreon account and use it to pledge to the first account’s page. A “per post” pledge will not incur any payments as long as it is cancelled before the end of the month.
- Use the API as needed.
Here’s an example of a campaign I use to test: https://www.patreon.com/patreonphp