Description:
Currently (version 4.11-1) the PKGBUILD for JUnit gets the sources from the archives on Kent Beck's GitHub account.
However, since it's last been updated, the repository has been moved to [1]. Kent Beck's repository has been either deleted or made private.
This matters because:
- there is no guarantee that Kent will keep the repository up-to-date, if at all;
- as evidenced at [2], since version 4.11 JUnit is distributed as one jar (junit.jar), instead of two (junit-dep.jar is gone). However, current ArchLinux version of the junit package ships with a junit-dep jar.

The reason for originally having two jars is that one of them (junit.jar) also packed a dependency (hamcrest), whereas junit-dep.jar was pure JUnit. Since JUnit version 4.11, they got rid of the junit+hamcrest package; one must now use proper dependency management tools to obtain hamcrest-core.jar (currently the dependency is on version 1.3).

There is an AUR package named 'hamcrest', but at the time of my writing this, it's out of date. (1.3RC2, while the current version of Hamcrest is just 1.3. I've flagged it.) To fix everything, it might be necessary to promote that package to the official repository.
However, there is a snag: aur/hamcrest does not pack a set of separate jars, but an all-inclusive hamcrest-all.jar. One could leave it as is, but it's not advisable due to possible Java classpath issues in applications with complex dependencies.

[1] https://github.com/junit-team/junit
[2] https://github.com/junit-team/junit/blob/master/doc/ReleaseNotes4.11.md#maven-artifacts

P.S.: it should also be noted that the 'url' field of the PKGBUILD is incorrect: www.junit.org does not exist, the correct link would be http://junit.org/.