using the rng created on the test instead the default rand (#5991)

Author: alanprot

pkg/ring/ring_test.go

@@ -2442,7 +2442,7 @@ func TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy(t *testing.T) {
 				t.Run(testName, func(t *testing.T) {
 					// Randomise the seed but log it in case we need to reproduce the test on failure.
 					seed := time.Now().UnixNano()
-					rand.New(rand.NewSource(seed))
+					rnd := rand.New(rand.NewSource(seed))
 					t.Log("random generator seed:", seed)
 
 					// Initialise the ring.
@@ -2485,7 +2485,7 @@ func TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy(t *testing.T) {
 					for i := 1; i <= numEvents; i++ {
 						currTime = currTime.Add(delayBetweenEvents)
 
-						switch r := rand.Intn(100); {
+						switch r := rnd.Intn(100); {
 						case r < 80:
 							// Scale up instances by 1.
 							instanceID := fmt.Sprintf("instance-%d", nextInstanceID)
@@ -2508,7 +2508,7 @@ func TestRing_ShuffleShardWithLookback_CorrectnessWithFuzzy(t *testing.T) {
 
 							sort.Strings(instanceIDs)
 
-							idxToRemove := rand.Intn(len(instanceIDs))
+							idxToRemove := rnd.Intn(len(instanceIDs))
 							idToRemove := instanceIDs[idxToRemove]
 							delete(ringDesc.Ingesters, idToRemove)