[client] Add unit tests for engine synchronization and Info flag copying

- Introduced tests for the Engine's handleSync method to verify behavior when SkipNetworkMapUpdate is true and when NetworkMap is nil.
- Added a test for the Info struct to ensure correct copying of flag values from one instance to another, while preserving unrelated fields.

client/internal/engine_sync_test.go

@@ -0,0 +1,79 @@
+package internal
+
+import (
+    "context"
+    "testing"
+
+    "golang.zx2c4.com/wireguard/wgctrl/wgtypes"
+
+    "github.com/netbirdio/netbird/client/iface"
+    "github.com/netbirdio/netbird/client/internal/peer"
+    "github.com/netbirdio/netbird/shared/management/client"
+    mgmtProto "github.com/netbirdio/netbird/shared/management/proto"
+)
+
+// Ensures handleSync exits early when SkipNetworkMapUpdate is true
+func TestEngine_HandleSync_SkipNetworkMapUpdate(t *testing.T) {
+    key, err := wgtypes.GeneratePrivateKey()
+    if err != nil {
+        t.Fatal(err)
+    }
+
+    ctx, cancel := context.WithCancel(context.Background())
+    defer cancel()
+
+    engine := NewEngine(ctx, cancel, nil, &client.MockClient{}, nil, &EngineConfig{
+        WgIfaceName:  "utun199",
+        WgAddr:       "100.70.0.1/24",
+        WgPrivateKey: key,
+        WgPort:       33100,
+        MTU:          iface.DefaultMTU,
+    }, MobileDependency{}, peer.NewRecorder("https://mgm"), nil)
+    engine.ctx = ctx
+
+    // Precondition
+    if engine.networkSerial != 0 {
+        t.Fatalf("unexpected initial serial: %d", engine.networkSerial)
+    }
+
+    resp := &mgmtProto.SyncResponse{
+        NetworkMap: &mgmtProto.NetworkMap{Serial: 42},
+        SkipNetworkMapUpdate: true,
+    }
+
+    if err := engine.handleSync(resp); err != nil {
+        t.Fatalf("handleSync returned error: %v", err)
+    }
+
+    if engine.networkSerial != 0 {
+        t.Fatalf("networkSerial changed despite SkipNetworkMapUpdate; got %d, want 0", engine.networkSerial)
+    }
+}
+
+// Ensures handleSync exits early when NetworkMap is nil
+func TestEngine_HandleSync_NilNetworkMap(t *testing.T) {
+    key, err := wgtypes.GeneratePrivateKey()
+    if err != nil {
+        t.Fatal(err)
+    }
+
+    ctx, cancel := context.WithCancel(context.Background())
+    defer cancel()
+
+    engine := NewEngine(ctx, cancel, nil, &client.MockClient{}, nil, &EngineConfig{
+        WgIfaceName:  "utun198",
+        WgAddr:       "100.70.0.2/24",
+        WgPrivateKey: key,
+        WgPort:       33101,
+        MTU:          iface.DefaultMTU,
+    }, MobileDependency{}, peer.NewRecorder("https://mgm"), nil)
+    engine.ctx = ctx
+
+    resp := &mgmtProto.SyncResponse{NetworkMap: nil}
+
+    if err := engine.handleSync(resp); err != nil {
+        t.Fatalf("handleSync returned error: %v", err)
+    }
+}
+
+

client/system/info_test.go

@@ -1,13 +1,72 @@
 package system
 
 import (
-	"context"
-	"testing"
+    "context"
+    "testing"
 
-	"github.com/stretchr/testify/assert"
-	"google.golang.org/grpc/metadata"
+    "github.com/stretchr/testify/assert"
+    "google.golang.org/grpc/metadata"
 )
 
+func TestInfo_CopyFlagsFrom(t *testing.T) {
+	origin := &Info{}
+	serverSSHAllowed := true
+	origin.SetFlags(
+		true,   // RosenpassEnabled
+		false,  // RosenpassPermissive
+		&serverSSHAllowed,
+		true,  // DisableClientRoutes
+		false, // DisableServerRoutes
+		true,  // DisableDNS
+		false, // DisableFirewall
+		true,  // BlockLANAccess
+		false, // BlockInbound
+		true,  // LazyConnectionEnabled
+	)
+
+	got := &Info{}
+	got.CopyFlagsFrom(origin)
+
+	if got.RosenpassEnabled != true {
+		t.Fatalf("RosenpassEnabled not copied: got %v", got.RosenpassEnabled)
+	}
+	if got.RosenpassPermissive != false {
+		t.Fatalf("RosenpassPermissive not copied: got %v", got.RosenpassPermissive)
+	}
+	if got.ServerSSHAllowed != true {
+		t.Fatalf("ServerSSHAllowed not copied: got %v", got.ServerSSHAllowed)
+	}
+	if got.DisableClientRoutes != true {
+		t.Fatalf("DisableClientRoutes not copied: got %v", got.DisableClientRoutes)
+	}
+	if got.DisableServerRoutes != false {
+		t.Fatalf("DisableServerRoutes not copied: got %v", got.DisableServerRoutes)
+	}
+	if got.DisableDNS != true {
+		t.Fatalf("DisableDNS not copied: got %v", got.DisableDNS)
+	}
+	if got.DisableFirewall != false {
+		t.Fatalf("DisableFirewall not copied: got %v", got.DisableFirewall)
+	}
+	if got.BlockLANAccess != true {
+		t.Fatalf("BlockLANAccess not copied: got %v", got.BlockLANAccess)
+	}
+	if got.BlockInbound != false {
+		t.Fatalf("BlockInbound not copied: got %v", got.BlockInbound)
+	}
+	if got.LazyConnectionEnabled != true {
+		t.Fatalf("LazyConnectionEnabled not copied: got %v", got.LazyConnectionEnabled)
+	}
+
+	// ensure CopyFlagsFrom does not touch unrelated fields
+	origin.Hostname = "host-a"
+	got.Hostname = "host-b"
+	got.CopyFlagsFrom(origin)
+	if got.Hostname != "host-b" {
+		t.Fatalf("CopyFlagsFrom should not overwrite non-flag fields, got Hostname=%q", got.Hostname)
+	}
+}
+
 func Test_LocalWTVersion(t *testing.T) {
 	got := GetInfo(context.TODO())
 	want := "development"