[bug] Fix datalayer Collector test flake

pkg/epp/datalayer/collector.go

@@ -83,10 +83,13 @@ func NewCollector() *Collector {
 
 // Start initiates data source collection for the endpoint.
 func (c *Collector) Start(ctx context.Context, ticker Ticker, ep Endpoint, sources []DataSource) error {
+	var ready chan struct{}
 	started := false
+
 	c.startOnce.Do(func() {
 		c.ctx, c.cancel = context.WithCancel(ctx)
 		started = true
+		ready = make(chan struct{})
 
 		go func(endpoint Endpoint, sources []DataSource) {
 			logger := log.FromContext(ctx).WithValues("endpoint", ep.GetPod().GetIPAddress())
@@ -97,6 +100,8 @@ func (c *Collector) Start(ctx context.Context, ticker Ticker, ep Endpoint, sourc
 				ticker.Stop()
 			}()
 
+			close(ready) // signal ready to accept ticks
+
 			for {
 				select {
 				case <-c.ctx.Done(): // per endpoint context cancelled
@@ -115,7 +120,21 @@ func (c *Collector) Start(ctx context.Context, ticker Ticker, ep Endpoint, sourc
 	if !started {
 		return errors.New("collector start called multiple times")
 	}
-	return nil
+
+	// Wait for goroutine to signal readiness.
+	// The use of ready channel is mostly to make the function testable, by ensuring
+	// synchronous order of events. Ignoring test requirements, one could let the
+	// go routine start at some arbitrary point in the future, possibly after this
+	// function has returned.
+	select {
+	case <-ready:
+		return nil
+	case <-ctx.Done():
+		if c.cancel != nil {
+			c.cancel() // ensure clean up
+		}
+		return ctx.Err()
+	}
 }
 
 // Stop terminates the collector.

pkg/epp/datalayer/collector_test.go

@@ -98,15 +98,16 @@ func TestCollectorCollectsOnTicks(t *testing.T) {
 	c := NewCollector()
 	ticker := mocks.NewTicker()
 	ctx := context.Background()
-	require.NoError(t, c.Start(ctx, ticker, endpoint, []DataSource{source}))
 
+	require.NoError(t, c.Start(ctx, ticker, endpoint, []DataSource{source}))
 	ticker.Tick()
 	ticker.Tick()
-	time.Sleep(20 * time.Millisecond) // let collector process the ticks
 
-	got := atomic.LoadInt64(&source.callCount)
-	want := int64(2)
-	assert.Equal(t, want, got, "call count mismatch")
+	// use Eventually for async processing
+	require.Eventually(t, func() bool {
+		return atomic.LoadInt64(&source.callCount) == 2
+	}, 1*time.Second, 2*time.Millisecond, "expected 2 collections")
+
 	require.NoError(t, c.Stop())
 }