JUnit was originally developed for Java, so I don't think auto-tagging with
lang-java would be inappropriate. The JUnit website doesn't even mention the word Scala, if my Google-fu is accurate.
I also believe that those using Scala are more adjusted to the idea that Java technologies can work with Scala. By contrast, many Java programmers will be unfamiliar with Scala and wouldn't know the distinction is required.
Whatever is decided, I've edited the junit tag excerpt to suggest the corresponding language tag is added.
To continue with the numbers started by blahdiblah in the comments (as of 16th Dec 2012):
- Total JUnit questions: 4,402
- of which tagged Java: 2,547 (58%)
- of which tagged Scala: 31 (0.7%)
- not tagged Java or Scala: 1,831 (42%)
Considering only the tagged questions, then 98.7% of all JUnit questions are Java-related. And note, this figure is likely to be corrupt in favour of Scala - Scala users are very likely to tag their questions appropriately because they are aware readers will assume they are using Java.
I think a language hint that suits at least 98% of the questions asked is quite appropriate. Especially when the minority group are more likely to tag their questions appropriately.