Extend the check in TestRun_AvoidNotifyWhenBehind to ensure we are

reading the full contents of each segment when reading segments that are
not the segment which is currently being written to.

Signed-off-by: Callum Styan <callumstyan@gmail.com>

tsdb/wlog/watcher_test.go

@@ -703,11 +703,11 @@ func TestRun_StartupTime(t *testing.T) {
 func TestRun_AvoidNotifyWhenBehind(t *testing.T) {
 	const pageSize = 32 * 1024
 	const segments = 10
-	const seriesCount = 20
-	const samplesCount = 300
+	const seriesCount = 10
+	const samplesCount = 85
 
 	// This test can take longer than intended to finish in cloud CI.
-	readTimeout := 10 * time.Second
+	readTimeout := 15 * time.Second
 
 	for _, compress := range []CompressionType{CompressionNone, CompressionSnappy, CompressionZstd} {
 		t.Run(string(compress), func(t *testing.T) {
@@ -745,11 +745,16 @@ func TestRun_AvoidNotifyWhenBehind(t *testing.T) {
 						require.NoError(t, w.Log(sample))
 					}
 				}
+				// Force creation of the next segment
+				w.NextSegment()
 			}
 			wg.Add(1)
+			var samplesAfterStart int
 			go func() {
 				defer wg.Done()
-				for i := 1; i < segments; i++ {
+				// add one more than max segment so that we can exit nicely
+				// when we get to the max segment value in the watcher
+				for i := 1; i < segments+1; i++ {
 					for j := 0; j < seriesCount; j++ {
 						ref := j + (i * 100)
 						series := enc.Series([]record.RefSeries{
@@ -769,9 +774,14 @@ func TestRun_AvoidNotifyWhenBehind(t *testing.T) {
 									V:   float64(i),
 								},
 							}, nil)
+							if w.segment.i <= segments {
+								samplesAfterStart++
+							}
 							require.NoError(t, w.Log(sample))
 						}
 					}
+					// Force creation of the next segment
+					w.NextSegment()
 				}
 			}()
 
@@ -781,16 +791,12 @@ func TestRun_AvoidNotifyWhenBehind(t *testing.T) {
 
 			watcher.setMetrics()
 			startTime := time.Now()
+
 			err = watcher.Run()
 			wg.Wait()
 			require.Less(t, time.Since(startTime), readTimeout)
 
-			// But samples records shouldn't get dropped
-			retry(t, defaultRetryInterval, defaultRetries, func() bool {
-				return wt.checkNumSeries() > 0
-			})
-			require.Greater(t, wt.samplesAppended, 0)
-
+			require.Eventually(t, func() bool { return samplesAfterStart == wt.samplesAppended }, readTimeout, time.Second, fmt.Sprintf("expected %d samples but saw %d", samplesAfterStart, wt.samplesAppended))
 			require.NoError(t, err)
 			require.NoError(t, w.Close())
 		})