feat(varlogtest): create new instance of admin and log

This PR makes the varlogtest return a new instance of admin client and log client when
`pkg/varlogtest.(*VarlogTest).Admin` and `pkg/varlogtest.(*VarlogTest).Log` are invoked.
Previously, those returned the same instances so callers shared them. However, it wasn't right
decision because the callers had to share the clients regardless their needs.

pkg/varlogtest/admin.go

@@ -23,14 +23,15 @@ import (
 )
 
 type testAdmin struct {
-	vt *VarlogTest
+	vt     *VarlogTest
+	closed bool
 }
 
 var _ varlog.Admin = (*testAdmin)(nil)
 
 func (c *testAdmin) lock() error {
 	c.vt.cond.L.Lock()
-	if c.vt.adminClientClosed {
+	if c.closed {
 		c.vt.cond.L.Unlock()
 		return verrors.ErrClosed
 	}
@@ -534,6 +535,6 @@ func (c *testAdmin) RemoveMRPeer(ctx context.Context, raftURL string, opts ...va
 func (c *testAdmin) Close() error {
 	c.vt.cond.L.Lock()
 	defer c.vt.cond.L.Unlock()
-	c.vt.adminClientClosed = true
+	c.closed = true
 	return nil
 }

pkg/varlogtest/log.go

@@ -14,14 +14,15 @@ import (
 )
 
 type testLog struct {
-	vt *VarlogTest
+	vt     *VarlogTest
+	closed bool
 }
 
 var _ varlog.Log = (*testLog)(nil)
 
 func (c *testLog) lock() error {
 	c.vt.cond.L.Lock()
-	if c.vt.varlogClientClosed {
+	if c.closed {
 		c.vt.cond.L.Unlock()
 		return verrors.ErrClosed
 	}
@@ -35,7 +36,7 @@ func (c *testLog) unlock() {
 func (c *testLog) Close() error {
 	c.vt.cond.L.Lock()
 	defer c.vt.cond.L.Unlock()
-	c.vt.varlogClientClosed = true
+	c.closed = true
 	c.vt.cond.Broadcast()
 	return nil
 }
@@ -247,7 +248,7 @@ func (c *testLog) SubscribeTo(ctx context.Context, topicID types.TopicID, logStr
 		return logEntries
 	}
 	s.vt.closedClient = func() bool {
-		return c.vt.varlogClientClosed
+		return c.closed
 	}
 
 	s.wg.Add(1)

pkg/varlogtest/varlogtest.go

@@ -17,9 +17,6 @@ import (
 type VarlogTest struct {
 	config
 
-	admin *testAdmin
-	vlg   *testLog
-
 	rng *rand.Rand
 
 	mu               sync.Mutex
@@ -38,9 +35,6 @@ type VarlogTest struct {
 	nextTopicID       types.TopicID
 	nextStorageNodeID types.StorageNodeID
 	nextLogStreamID   types.LogStreamID
-
-	adminClientClosed  bool
-	varlogClientClosed bool
 }
 
 func New(opts ...Option) (*VarlogTest, error) {
@@ -62,8 +56,6 @@ func New(opts ...Option) (*VarlogTest, error) {
 		leaderMR:         types.InvalidNodeID,
 	}
 	vt.cond = sync.NewCond(&vt.mu)
-	vt.admin = &testAdmin{vt: vt}
-	vt.vlg = &testLog{vt: vt}
 
 	for _, mrn := range vt.initialMRNodes {
 		if vt.leaderMR == types.InvalidNodeID {
@@ -77,11 +69,11 @@ func New(opts ...Option) (*VarlogTest, error) {
 }
 
 func (vt *VarlogTest) Admin() varlog.Admin {
-	return vt.admin
+	return &testAdmin{vt: vt}
 }
 
 func (vt *VarlogTest) Log() varlog.Log {
-	return vt.vlg
+	return &testLog{vt: vt}
 }
 
 func (vt *VarlogTest) generateTopicID() types.TopicID {