It seems (http://jxcl.sourceforge.net/tutorials/ant.html) that in order to use JUnit with Ant, junit.jar must be in the ant lib dir during build. The /usr/lib/ant-junit.jar from the arch package has no classes in it, only xls files - it needs the JUnitTask.class and a few more to work with JUnit. It is only an optional ant task, but still it would be nice to have it working after installing apache-ant, and I think most people who use ant, use JUnit too.

I have modified the PKGBUILD to build with JUnit:

pkgname=apache-ant
pkgver=1.6.1
pkgrel=2
pkgdesc="Ant is a java-based build tool."
depends=(j2sdk)
source=(http://apache.mirror.mcgill.ca/ant/source/$pkgname-$pkgver-src.tar.gz
http://belnet.dl.sourceforge.net/sourceforge/junit/junit3.8.1.zip)
md5sums=('e6276665f1c09fcdf47b8f7900b4a531' '5110326e4b7f7497dfa60ede4b626751')
url="http://ant.apache.org/"

build() {
cp $startdir/src/junit3.8.1/junit.jar $startdir/src/$pkgname-$pkgver/lib
cd $startdir/src/$pkgname-$pkgver
mkdir dist
./build.sh -Ddist.dir=dist/ dist
export ANT_HOME="$startdir/pkg/usr"
./build.sh install-lite
}