I've left the issues open because they haven't been resolved. The author hasn't been on since February, so the author may fix it in due time. It gives you notifications if there is an issue, so the author can look at them when they get back; your comment wasn't marked as an issue so it's less likely that the author may see it also.

Read the comments next time.

In the Java testcases, the expected and the actual are swapped around, so your solution is returning 0 and the expected answer is 7.

Proven by the testcase

assertEquals( "Nope!" , DRoot.digital_root(16), 7);