tests/misc: Poll journal for error message

We could race in having the client error out and try querying the journal
before the daemon had written the error message.

Closes: #3075

tests/common/libtest.sh

@@ -447,6 +447,21 @@ rpmostree_assert_status() {
     rm -f status.json
 }
 
+# Wait for a non-empty result from journalctl.
+# It's recommended to use arguments like this to search
+# for a message from a specific service `--after-cursor <cursor> --grep=message -u rpm-ostreed`.
+journal_poll() {
+    timeout=60
+    for x in $(seq $timeout); do
+      if journalctl -q -n 1 "$@"; then
+        return
+      fi
+      sleep 1
+    done
+    echo "timed out waiting $timeout seconds for journalctl $@" 1>&2
+    exit 1
+}
+
 # This function below was taken and adapted from coreos-assembler. We
 # should look into sharing this code more easily.
 

tests/kolainst/nondestructive/misc.sh

@@ -109,8 +109,7 @@ if env FAILPOINTS='client::connect=return(synthetic-error)' rpm-ostree initramfs
     fatal "should have errored"
 fi
 assert_file_has_content_literal err.txt "error: synthetic-error"
-journalctl -u rpm-ostreed --after-cursor "${cursor}" > out.txt
-assert_file_has_content_literal out.txt 'client disconnected before calling Start'
+journal_poll -u rpm-ostreed --after-cursor "${cursor}" --grep="client disconnected before calling Start"
 rpm-ostree status > out.txt
 assert_file_has_content_literal out.txt 'State: idle'
 echo "ok auto-cancel not-started transaction"