br/pkg/streamhelper: fix flaky TestGCServiceSafePoint assertion (pingcap#66755)

close pingcap#66731

Author: v01dstar

br/pkg/streamhelper/advancer_test.go

@@ -209,12 +209,15 @@ func TestGCServiceSafePoint(t *testing.T) {
 
 	req.NoError(adv.OnTick(ctx))
 	req.Equal(env.serviceGCSafePoint, cp-1)
+	env.fakeCluster.mu.Lock()
+	req.True(env.serviceGCSafePointSet)
+	env.fakeCluster.mu.Unlock()
 
 	env.unregisterTask()
 	req.Eventually(func() bool {
 		env.fakeCluster.mu.Lock()
 		defer env.fakeCluster.mu.Unlock()
-		return env.serviceGCSafePoint != 0 && env.serviceGCSafePointDeleted
+		return env.serviceGCSafePointDeleted
 	}, 3*time.Second, 100*time.Millisecond)
 }
 

br/pkg/streamhelper/basic_lib_for_test.go

@@ -108,6 +108,7 @@ type fakeCluster struct {
 	onGetClient               func(uint64) error
 	onClearCache              func(uint64) error
 	serviceGCSafePoint        uint64
+	serviceGCSafePointSet     bool
 	serviceGCSafePointDeleted bool
 	currentTS                 uint64
 }
@@ -279,6 +280,7 @@ func (f *fakeCluster) BlockGCUntil(ctx context.Context, at uint64) (uint64, erro
 		return f.serviceGCSafePoint, errors.Errorf("minimal safe point %d is greater than the target %d", f.serviceGCSafePoint, at)
 	}
 	f.serviceGCSafePoint = at
+	f.serviceGCSafePointSet = true
 	return at, nil
 }