test-history: Skip test if we cannot read from the Journal

In some OS configurations, unprivileged users cannot read back messages
that they have written to the system log. This test cannot succeed if that
happens, so skip it.

In particular, if the Journal is only in-memory rather than persisted
to disk (as it was by default in Debian 10), then there are no per-user
Journal files, only a single system-wide Journal which requires privileges
to read.

Signed-off-by: Simon McVittie <smcv@collabora.com>
Fixes: 8b05f6b3 "Add a unit test for the history command"

tests/test-history.sh

@@ -11,11 +11,21 @@ USE_SYSTEMDIR=yes
 skip_without_bwrap
 skip_revokefs_without_fuse
 
-echo "1..1"
-
 HISTORY_START_TIME=$(date +"%Y-%m-%d %H:%M:%S")
 sleep 1
 
+if ! logger "Checking whether Flatpak can use the journal..."; then
+    skip "Cannot write to Journal with logger"
+fi
+
+messages="$(journalctl --user --since="${HISTORY_START_TIME}" || true)"
+
+if [ -z "$messages" ]; then
+    skip "Cannot read back from Journal with journalctl"
+fi
+
+echo "1..1"
+
 mkdir -p ${TEST_DATA_DIR}/system-history-installation
 mkdir -p ${FLATPAK_CONFIG_DIR}/installations.d
 cat << EOF > ${FLATPAK_CONFIG_DIR}/installations.d/history-installation.conf