[#1320] test: Fix TestGCDropsObjectInhumedFromWritecache flaky test

The `TestGCDropsObjectInhumedFromWritecache` test was flaky because a
running asynchronous rebuild operation prevented GC from deleting the
object. A test-only shard option `WithDisabledRebuild` has been added
to fix this.

Signed-off-by: Aleksey Savchuk <a.savchuk@yadro.com>

pkg/local_object_storage/shard/control.go

@@ -130,7 +130,7 @@ func (s *Shard) Init(ctx context.Context) error {
 	s.gc.init(ctx)
 
 	s.rb = newRebuilder(s.rebuildLimiter)
-	if !m.NoMetabase() {
+	if !m.NoMetabase() && !s.rebuildDisabled {
 		s.rb.Start(ctx, s.blobStor, s.metaBase, s.log)
 	}
 	s.writecacheSealCancel.Store(dummyCancel)
@@ -398,7 +398,7 @@ func (s *Shard) Reload(ctx context.Context, opts ...Option) error {
 	defer unlock()
 
 	s.rb.Stop(s.log)
-	if !s.info.Mode.NoMetabase() {
+	if !s.info.Mode.NoMetabase() && !s.rebuildDisabled {
 		defer func() {
 			s.rb.Start(ctx, s.blobStor, s.metaBase, s.log)
 		}()

pkg/local_object_storage/shard/gc_test.go

@@ -187,7 +187,7 @@ func TestGCDropsObjectInhumedFromWritecache(t *testing.T) {
 
 func testGCDropsObjectInhumedFromWritecache(t *testing.T, flushbeforeInhume bool) {
 	sh := newCustomShard(t, true, shardOptions{
-		additionalShardOptions: []Option{WithDisabledGC()},
+		additionalShardOptions: []Option{WithDisabledGC(), WithDisabledRebuild()},
 		wcOpts:                 []writecache.Option{writecache.WithDisableBackgroundFlush()},
 	})
 	defer func() { require.NoError(t, sh.Close()) }()

pkg/local_object_storage/shard/shard.go

@@ -139,6 +139,8 @@ type cfg struct {
 	reportErrorFunc func(selfID string, message string, err error)
 
 	rebuildLimiter RebuildWorkerLimiter
+
+	rebuildDisabled bool
 }
 
 func defaultCfg() *cfg {
@@ -410,6 +412,14 @@ func WithZeroCountCallback(cb EmptyContainersCallback) Option {
 	}
 }
 
+// WithDisabledRebuild returns an option to disable a shard rebuild.
+// For testing purposes only.
+func WithDisabledRebuild() Option {
+	return func(c *cfg) {
+		c.rebuildDisabled = true
+	}
+}
+
 func (s *Shard) fillInfo() {
 	s.cfg.info.MetaBaseInfo = s.metaBase.DumpInfo()
 	s.cfg.info.BlobStorInfo = s.blobStor.DumpInfo()