The first API for automating your tests for Hreflang is now here. You can submit URLs as a list or submit a sitemap URL to test all pages in the sitemap. When you submit a test, the response contains a test ID. You can later query for the status of the test. If a test is completed, you can query for the results of the test.
Read the Hreflang testing API Docs.
Once you log in and generate an API key, you can use it in the API playground.