add debug log an fix flaky test (#4290)

- add debug logs on Manager.update for completeness
 - Refactor and rename TestManager_OutputChange
    - use eventually instead of time.Sleep
    - rename to better reflect what it tests
 - Remove TestManager_StartStop as TestManager_StartStopComponent already covers it

(cherry picked from commit a5262e1)

pkg/component/runtime/manager.go

@@ -772,24 +772,27 @@ func (m *Manager) update(model component.Model, teardown bool) error {
 		stop = append(stop, existing)
 	}
 	m.currentMx.RUnlock()
-	if len(stop) > 0 {
-		var stoppedWg sync.WaitGroup
-		stoppedWg.Add(len(stop))
-		for _, existing := range stop {
-			m.logger.Debugf("Stopping component %q", existing.id)
-			_ = existing.stop(teardown, model.Signed)
-			// stop is async, wait for operation to finish,
-			// otherwise new instance may be started and components
-			// may fight for resources (e.g ports, files, locks)
-			go func(state *componentRuntimeState) {
-				m.waitForStopped(state)
-				stoppedWg.Done()
-			}(existing)
-		}
-		stoppedWg.Wait()
+
+	var stoppedWg sync.WaitGroup
+	stoppedWg.Add(len(stop))
+	for _, existing := range stop {
+		m.logger.Debugf("Stopping component %q", existing.id)
+		_ = existing.stop(teardown, model.Signed)
+		// stop is async, wait for operation to finish,
+		// otherwise new instance may be started and components
+		// may fight for resources (e.g. ports, files, locks)
+		go func(state *componentRuntimeState) {
+			err := m.waitForStopped(state)
+			if err != nil {
+				m.logger.Errorf("updating components: failed waiting %s stop",
+					state.id)
+			}
+			stoppedWg.Done()
+		}(existing)
 	}
+	stoppedWg.Wait()
 
-	// start all not started
+	// start new components
 	for _, comp := range newComponents {
 		// new component; create its runtime
 		logger := m.baseLogger.Named(fmt.Sprintf("component.runtime.%s", comp.ID))
@@ -800,6 +803,7 @@ func (m *Manager) update(model component.Model, teardown bool) error {
 		m.currentMx.Lock()
 		m.current[comp.ID] = state
 		m.currentMx.Unlock()
+		m.logger.Debugf("Starting component %q", comp.ID)
 		if err = state.start(); err != nil {
 			return fmt.Errorf("failed to start component %s: %w", comp.ID, err)
 		}
@@ -808,10 +812,11 @@ func (m *Manager) update(model component.Model, teardown bool) error {
 	return nil
 }
 
-func (m *Manager) waitForStopped(comp *componentRuntimeState) {
+func (m *Manager) waitForStopped(comp *componentRuntimeState) error {
 	if comp == nil {
-		return
+		return nil
 	}
+
 	currComp := comp.getCurrent()
 	compID := currComp.ID
 	timeout := defaultStopTimeout
@@ -828,20 +833,23 @@ func (m *Manager) waitForStopped(comp *componentRuntimeState) {
 		latestState := comp.getLatest()
 		if latestState.State == client.UnitStateStopped {
 			m.logger.Debugf("component %q stopped.", compID)
-			return
+			return nil
 		}
 
+		// it might happen the component stop signal isn't received but the
+		// manager detects it stopped running. Then the manager removes it from
+		// its list of current components. Therefore, we also need to check if
+		// the component was removed, if it was, we consider it stopped.
 		m.currentMx.RLock()
 		if _, exists := m.current[compID]; !exists {
 			m.currentMx.RUnlock()
-			return
+			return nil
 		}
 		m.currentMx.RUnlock()
 
 		select {
 		case <-timeoutCh:
-			m.logger.Errorf("timeout exceeded waiting for component %q to stop", compID)
-			return
+			return fmt.Errorf("timeout exceeded after %s", timeout)
 		case <-time.After(stopCheckRetryPeriod):
 		}
 	}