[wpilib] OpModeRobot: set up notifier before calling observe starting (#8547)

This avoids a simulation race.

wpilibj/src/main/java/org/wpilib/framework/OpModeRobot.java

@@ -566,7 +566,6 @@ public abstract class OpModeRobot extends RobotBase {
   @Override
   public final void startCompetition() {
     System.out.println("********** Robot program startup complete **********");
-    DriverStationJNI.observeUserProgramStarting();
 
     int event = WPIUtilJNI.createEvent(false, false);
     DriverStationJNI.provideNewDataEventHandle(event);
@@ -577,11 +576,22 @@ public abstract class OpModeRobot extends RobotBase {
     try {
       // Implement the opmode lifecycle
       long lastModeId = -1;
+      boolean calledObserveUserProgramStarting = false;
       boolean calledDriverStationConnected = false;
       int[] events = {event, m_notifier};
       while (true) {
         // Wait for new data from the driver station, with 50 ms timeout
         NotifierJNI.setNotifierAlarm(m_notifier, 50000, 0, false, true);
+
+        // Call observeUserProgramStarting() here as a one-shot to ensure it is called after the
+        // notifier alarm is set.  The notifier alarm is set using relative time, so tests that
+        // wait on the user program to start and then step time won't work correctly if we call
+        // this before setting the alarm.
+        if (!calledObserveUserProgramStarting) {
+          calledObserveUserProgramStarting = true;
+          DriverStationJNI.observeUserProgramStarting();
+        }
+
         try {
           int[] signaled = WPIUtilJNI.waitForObjects(events);
           for (int val : signaled) {