So you are writing a plugin? Sorry it's unclear to me.
If you are doing so, I'd run integration tests using the elasticsearch test framework.
Then you can attach elasticsearch code source to your project and add breakpoints in it (or better in your code).
BTW, working on a non stable version of elasticsearch (like master branch) does not look to me as the best thing to do.
I'm only doing so iif the latest version does not contain a patch I absolutely need. In which case, I'm building my local version which I'm using in integration tests.
My 2 cents.