There are several apps on the market to test APIs with. A quite nice one I just stubled opon is called Postman. It's first of all a Chrome extension, but it's also already available as a Chrome App and therefore as a packaged app which can be started on the Mac as any other Mac app.
You're able to group single calls to collections and therefore save and manage them. With the Jetpacks option you can even run multiple calls at once and automatise testing with data variables.
Those collections are also the starting point when you want to work with a team. You can import and export all calls in one collection or even the complete data set.
The app also offers a few helpers regarding header informationen, like Basic Auth or OAuth.
If you search for a tool for API testing, just give it a try.