Not sure how I missed this, but we of course need to wait for the
"systemd-run" commands to finish before we can check the output files
this generated.
systemd-analyze set-log-level debug
systemd-analyze set-log-target console
-systemd-run --unit=one -p StandardOutput=file:/tmp/stdout -p StandardError=file:/tmp/stderr -p Type=exec sh -c 'echo x ; echo y >&2'
+systemd-run --wait --unit=one -p StandardOutput=file:/tmp/stdout -p StandardError=file:/tmp/stderr -p Type=exec sh -c 'echo x ; echo y >&2'
cmp /tmp/stdout <<EOF
x
EOF
y
EOF
-systemd-run --unit=two -p StandardOutput=file:/tmp/stdout -p StandardError=file:/tmp/stderr -p Type=exec sh -c 'echo z ; echo a >&2'
+systemd-run --wait --unit=two -p StandardOutput=file:/tmp/stdout -p StandardError=file:/tmp/stderr -p Type=exec sh -c 'echo z ; echo a >&2'
cmp /tmp/stdout <<EOF
z
EOF
a
EOF
-systemd-run --unit=three -p StandardOutput=append:/tmp/stdout -p StandardError=append:/tmp/stderr -p Type=exec sh -c 'echo b ; echo c >&2'
+systemd-run --wait --unit=three -p StandardOutput=append:/tmp/stdout -p StandardError=append:/tmp/stderr -p Type=exec sh -c 'echo b ; echo c >&2'
cmp /tmp/stdout <<EOF
z
b