The last line of tests/guix-system.sh is:

guix system -n docker-image gnu/system/examples/docker-image.tmpl

It doesn't work when building from guix-1.0.0.tar.gz because the file gnu/system/examples/docker-image.tmpl doesn't exist in the source tarball. If I manually download the file from the git repository and put it into the extracted source tree, the test passes.