Why make it human readable?

Especially if you want lots of providers to support it, pick something super easy to parse.. JSON is the obvious choice there:

   [{ method: "GET",
      url: "index.html",
      tests: [ contains: "nyaruka",
               response_in_ms: 500,
               status: 200 ] },
    { method: "POST",
      url: "login.html",
      params: { foo: "bar" }
      tests: [ "status": 200 ] }]