kvserver: deflake TestRefreshPolicyWithVariousLatencies

TestRefreshPolicyWithVariousLatencies verifies RefreshPolicy logic using a test
latencies map.

It was previously flaky due to: 1. not waiting for SetSpanConfig to take effect
before invoking RefreshPolicy, which could trigger the background policy
refresher during the test, and 2. background RefreshPolicy calls on leaseholder
replicas interfering with the test.

This commit resolves both issues by: 1. using SucceedsSoon to wait for
SetSpanConfig to take effect, and 2. invoking RefreshPolicy on a non-leaseholder
replica instead.

Epic: none
Release note: none

Author: wenyihu6

pkg/kv/kvserver/replica_closedts_test.go

@@ -1119,16 +1119,30 @@ func TestRefreshPolicyWithVariousLatencies(t *testing.T) {
 	defer log.Scope(t).Close(t)
 
 	ctx := context.Background()
-	tc := testcluster.StartTestCluster(t, 3, base.TestClusterArgs{})
+	tc := testcluster.StartTestCluster(t, 3, base.TestClusterArgs{
+		ReplicationMode: base.ReplicationManual,
+	})
 	defer tc.Stopper().Stop(ctx)
 
 	// Create a scratch range.
 	scratchKey := tc.ScratchRange(t)
-	store := tc.GetFirstStoreFromServer(t, 0)
+	tc.AddVotersOrFatal(t, scratchKey, tc.Targets(1, 2)...)
+
+	// Get a non-leaseholder replica to avoid background RefreshPolicy calls that
+	// would interfere with testing the policy refresh logic in isolation.
+	store := tc.GetFirstStoreFromServer(t, 1)
 	repl := store.LookupReplica(roachpb.RKey(scratchKey))
 	require.NotNil(t, repl)
 	repl.SetSpanConfig(roachpb.SpanConfig{GlobalReads: true}, roachpb.Span{Key: scratchKey})
 
+	// Verify that the range is properly configured to use global reads.
+	testutils.SucceedsSoon(t, func() error {
+		if repl.GetRangeInfo(ctx).ClosedTimestampPolicy != roachpb.LEAD_FOR_GLOBAL_READS {
+			return errors.New("expected LEAD_FOR_GLOBAL_READS")
+		}
+		return nil
+	})
+
 	// Define test cases with different latency scenarios.
 	testCases := []struct {
 		name           string