tests: use stop/start over restart for service

systemctl restart does not wait for all file descriptors to be flushed before returning which is most likely the reason why some pid information is still being detected via pgrep -f. Using stop/start does not suffer from this problem...but time will tell.

Author: reubenmiller

tests/RobotFramework/tests/configuration/lock_file.robot

@@ -28,8 +28,8 @@ Check PID number in lock file
 Check PID number in lock file after restarting the services
     [Documentation]    Include the new pid generated after service restart 
     ...  inside the existing lock files under /run/lock/
-    Restart Service    tedge-agent
-    Restart Service    tedge-mapper-c8y
+    Stop/Start Service    tedge-agent
+    Stop/Start Service    tedge-mapper-c8y
     ${pid_agent2}=    Execute Command    pgrep -f '^/usr/bin/tedge-agent'    strip=True
     ${pid_mapper2}=    Execute Command    pgrep -f '^/usr/bin/tedge-mapper c8y'    strip=${True}
     ${pid_agent_lock2}=    Execute Command    cat /run/lock/tedge-agent.lock
@@ -61,3 +61,13 @@ Switch off lock file creation
     #Check that no lock file is created
     File Should Not Exist    /run/lock/tedge-agent.lock
     File Should Not Exist    /run/lock/tedge-mapper-c8y.lock
+
+*** Keywords ***
+
+Stop/Start Service
+    [Arguments]    ${name}
+    # Note: Use stop/start service rather than restart as 'systemctl restart <service>'
+    # does not wait for all file descriptors to be flushed before returning, https://man7.org/linux/man-pages/man1/systemctl.1.html
+    # See https://github.com/thin-edge/thin-edge.io/issues/2087 for more details
+    Stop Service    ${name}
+    Start Service    ${name}