testsuite-77: Fix race condition

Use a socket unit to make sure the socket exists before we start
the client that accesses it.

test/units/testsuite-77-netcat.service

@@ -1,7 +0,0 @@
-# SPDX-License-Identifier: LGPL-2.1-or-later
-[Unit]
-Description=TEST-77-OPENFILE
-
-[Service]
-ExecStart=/usr/lib/systemd/tests/testdata/units/%N.sh
-Type=simple

test/units/testsuite-77-netcat.sh

@@ -1,4 +0,0 @@
-#!/usr/bin/env bash
-# SPDX-License-Identifier: LGPL-2.1-or-later
-
-echo "Socket" | nc -lkU /tmp/test.sock

test/units/testsuite-77-server.socket

@@ -0,0 +1,6 @@
+[Unit]
+Description=TEST-77-OPENFILE server socket
+
+[Socket]
+ListenStream=/tmp/test.sock
+Accept=yes

test/units/testsuite-77-server@.service

@@ -0,0 +1,7 @@
+[Unit]
+Description=TEST-77-OPENFILE server
+
+[Service]
+ExecStart=echo "Socket"
+StandardInput=socket
+StandardOutput=socket

test/units/testsuite-77-socket.service

@@ -1,9 +0,0 @@
-# SPDX-License-Identifier: LGPL-2.1-or-later
-[Unit]
-Description=TEST-77-OPENFILE
-
-[Service]
-OpenFile=/tmp/test.sock:socket:read-only
-ExecStartPre=rm -f /failed /testok
-ExecStart=/usr/lib/systemd/tests/testdata/units/%N.sh
-Type=oneshot

test/units/testsuite-77.sh

@@ -16,8 +16,11 @@ read -r -u 4 text
 assert_eq "$text" "File"
 
 # Test for socket
-systemctl start testsuite-77-netcat.service
-systemctl start testsuite-77-socket.service
+systemctl start testsuite-77-server.socket
+systemd-run -p OpenFile=/tmp/test.sock:socket:read-only \
+            --wait \
+            --pipe \
+            /usr/lib/systemd/tests/testdata/units/testsuite-77-client.sh
 
 # Tests for D-Bus
 diff <(systemctl show -p OpenFile testsuite-77) - <<EOF