There is no real reason for these packages to conflict.
There are very good reasons to have both installed simultaneously.

Most unit-test's are implemented at the module level so all files are separate.
The only conflicts are:

/usr/man/man1/nosetests.1.gz
/usr/bin/nosetests

## The fix is to add the following line to the PKGBUILD

package_python2-nose() {
...
rm -rf "$pkgdir/usr/bin/nosetests" "$pkgdir"/usr/share
}



package_python-nose-doc(){
pkgdesc="Nose documentation and examples"

cd "$srcdir/nose-$pkgver/doc"
make html
mkdir -p "$pkgdir/usr/share/doc/python-nose"
cp -r .build/html "$pkgdir/usr/share/doc/python-nose"
cp -r ../examples "$pkgdir/usr/share/doc/python-nose"
}