diff --git a/core/blockchain_stats_test.go b/core/blockchain_stats_test.go
new file mode 100644
index 0000000000..7e64a9b1b9
--- /dev/null
+++ b/core/blockchain_stats_test.go
@@ -0,0 +1,258 @@
+// Copyright 2026 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package core
+
+import (
+	"encoding/json"
+	"math/big"
+	"testing"
+	"time"
+
+	"github.com/ethereum/go-ethereum/core/state"
+	"github.com/ethereum/go-ethereum/core/types"
+)
+
+// TestStateCountsAdd locks down the count merge primitive used to aggregate
+// per-tx, pre-tx and post-tx counters in the BAL parallel path.
+func TestStateCountsAdd(t *testing.T) {
+	a := state.StateCounts{
+		AccountLoaded:   1,
+		AccountUpdated:  2,
+		AccountDeleted:  3,
+		StorageLoaded:   4,
+		StorageUpdated:  5,
+		StorageDeleted:  6,
+		CodeLoaded:      7,
+		CodeLoadBytes:   8,
+		CodeUpdated:     9,
+		CodeUpdateBytes: 10,
+	}
+	b := state.StateCounts{
+		AccountLoaded:   100,
+		AccountUpdated:  200,
+		AccountDeleted:  300,
+		StorageLoaded:   400,
+		StorageUpdated:  500,
+		StorageDeleted:  600,
+		CodeLoaded:      700,
+		CodeLoadBytes:   800,
+		CodeUpdated:     900,
+		CodeUpdateBytes: 1000,
+	}
+	a.Add(&b)
+	want := state.StateCounts{
+		AccountLoaded:   101,
+		AccountUpdated:  202,
+		AccountDeleted:  303,
+		StorageLoaded:   404,
+		StorageUpdated:  505,
+		StorageDeleted:  606,
+		CodeLoaded:      707,
+		CodeLoadBytes:   808,
+		CodeUpdated:     909,
+		CodeUpdateBytes: 1010,
+	}
+	if a != want {
+		t.Fatalf("Add mismatch: got %+v, want %+v", a, want)
+	}
+}
+
+// fixtureBlock builds a minimal *types.Block usable as the slow-block log
+// subject. Only the header fields read by buildSlowBlockLog matter
+// (Number, GasUsed, plus Transactions count via Body).
+func fixtureBlock(number uint64, gasUsed uint64) *types.Block {
+	header := &types.Header{
+		Number:  new(big.Int).SetUint64(number),
+		GasUsed: gasUsed,
+	}
+	return types.NewBlockWithHeader(header)
+}
+
+// TestBuildSlowBlockLog_NonBALShape ensures non-BAL output doesn't include
+// the optional `bal` block (omitempty contract).
+func TestBuildSlowBlockLog_NonBALShape(t *testing.T) {
+	stats := &ExecuteStats{
+		AccountReads:  3 * time.Millisecond,
+		StorageReads:  4 * time.Millisecond,
+		AccountHashes: 5 * time.Millisecond,
+		Execution:     7 * time.Millisecond,
+		TotalTime:     20 * time.Millisecond,
+		MgasPerSecond: 12.5,
+		StateCounts: state.StateCounts{
+			AccountLoaded:  9,
+			StorageLoaded:  21,
+			StorageUpdated: 42,
+		},
+		// balTransitionStats deliberately nil — non-BAL block.
+	}
+	block := fixtureBlock(1234, 21000)
+	logEntry := buildSlowBlockLog(stats, block)
+
+	if logEntry.BAL != nil {
+		t.Fatalf("non-BAL log unexpectedly has bal extension: %+v", logEntry.BAL)
+	}
+	jsonBytes, err := json.Marshal(logEntry)
+	if err != nil {
+		t.Fatalf("marshal failed: %v", err)
+	}
+	var decoded map[string]any
+	if err := json.Unmarshal(jsonBytes, &decoded); err != nil {
+		t.Fatalf("unmarshal failed: %v", err)
+	}
+	wantKeys := map[string]bool{
+		"level": true, "msg": true, "block": true, "timing": true,
+		"throughput": true, "state_reads": true, "state_writes": true, "cache": true,
+	}
+	for k := range decoded {
+		if !wantKeys[k] {
+			t.Errorf("unexpected top-level key %q in non-BAL output (full JSON: %s)", k, string(jsonBytes))
+		}
+		delete(wantKeys, k)
+	}
+	if len(wantKeys) != 0 {
+		t.Errorf("missing top-level keys: %v", wantKeys)
+	}
+	// Spot-check a count field that exercises the int64→int conversion in
+	// state_writes.storage_slots (StorageUpdated is int64 on StateCounts).
+	writes := decoded["state_writes"].(map[string]any)
+	if got := writes["storage_slots"].(float64); got != 42 {
+		t.Errorf("storage_slots: got %v, want 42", got)
+	}
+}
+
+// TestBuildSlowBlockLog_BALShape ensures BAL output includes the bal extension
+// with all expected sub-keys.
+func TestBuildSlowBlockLog_BALShape(t *testing.T) {
+	balMetrics := &state.BALStateTransitionMetrics{
+		StatePrefetch:   1 * time.Millisecond,
+		AccountUpdate:   2 * time.Millisecond,
+		StateUpdate:     3 * time.Millisecond,
+		StateHash:       4 * time.Millisecond,
+		AccountCommits:  5 * time.Millisecond,
+		StorageCommits:  6 * time.Millisecond,
+		TrieDBCommits:   7 * time.Millisecond,
+		SnapshotCommits: 8 * time.Millisecond,
+	}
+	stats := &ExecuteStats{
+		AccountReads:       11 * time.Millisecond,
+		StorageReads:       22 * time.Millisecond,
+		CodeReads:          3 * time.Millisecond,
+		Execution:          15 * time.Millisecond,
+		TotalTime:          20 * time.Millisecond,
+		MgasPerSecond:      30.0,
+		ExecWall:           15 * time.Millisecond,
+		PostProcess:        2 * time.Millisecond,
+		Prefetch:           1 * time.Millisecond,
+		balTransitionStats: balMetrics,
+		StateCounts: state.StateCounts{
+			AccountUpdated:  3,
+			AccountDeleted:  1,
+			CodeUpdated:     2,
+			CodeUpdateBytes: 1024,
+		},
+		StateReadCacheStats: state.ReaderStats{
+			StateStats: state.StateReaderStats{
+				AccountCacheHit:  10,
+				AccountCacheMiss: 5,
+				StorageCacheHit:  20,
+				StorageCacheMiss: 8,
+			},
+		},
+	}
+	block := fixtureBlock(7, 100000)
+	logEntry := buildSlowBlockLog(stats, block)
+
+	if logEntry.BAL == nil {
+		t.Fatal("BAL log missing the bal extension")
+	}
+	jsonBytes, err := json.Marshal(logEntry)
+	if err != nil {
+		t.Fatalf("marshal failed: %v", err)
+	}
+	var decoded map[string]any
+	if err := json.Unmarshal(jsonBytes, &decoded); err != nil {
+		t.Fatalf("unmarshal failed: %v", err)
+	}
+	bal, ok := decoded["bal"].(map[string]any)
+	if !ok {
+		t.Fatalf("bal key not present in JSON or wrong type; full JSON: %s", string(jsonBytes))
+	}
+	wantSubkeys := []string{
+		"exec_wall_ms", "post_process_ms", "prefetch_ms",
+		"state_prefetch_ms", "account_update_ms", "state_update_ms", "state_hash_ms",
+		"account_commit_ms", "storage_commit_ms", "triedb_commit_ms", "snapshot_commit_ms",
+	}
+	for _, k := range wantSubkeys {
+		if _, present := bal[k]; !present {
+			t.Errorf("bal extension missing key %q", k)
+		}
+	}
+	// Spot-check a value: exec_wall_ms should be 15.0 (15ms).
+	if got := bal["exec_wall_ms"].(float64); got != 15.0 {
+		t.Errorf("exec_wall_ms: got %v, want 15.0", got)
+	}
+
+	// state_read_ms = AccountReads + StorageReads + CodeReads = 11 + 22 + 3 = 36 ms
+	timing := decoded["timing"].(map[string]any)
+	if got := timing["state_read_ms"].(float64); got != 36 {
+		t.Errorf("timing.state_read_ms: got %v, want 36", got)
+	}
+
+	writes := decoded["state_writes"].(map[string]any)
+	if got := writes["accounts"].(float64); got != 3 {
+		t.Errorf("state_writes.accounts: got %v, want 3", got)
+	}
+	if got := writes["accounts_deleted"].(float64); got != 1 {
+		t.Errorf("state_writes.accounts_deleted: got %v, want 1", got)
+	}
+	if got := writes["code"].(float64); got != 2 {
+		t.Errorf("state_writes.code: got %v, want 2", got)
+	}
+	if got := writes["code_bytes"].(float64); got != 1024 {
+		t.Errorf("state_writes.code_bytes: got %v, want 1024", got)
+	}
+
+	cache := decoded["cache"].(map[string]any)
+	acct := cache["account"].(map[string]any)
+	if got := acct["hits"].(float64); got != 10 {
+		t.Errorf("cache.account.hits: got %v, want 10", got)
+	}
+	if got := acct["misses"].(float64); got != 5 {
+		t.Errorf("cache.account.misses: got %v, want 5", got)
+	}
+	storage := cache["storage"].(map[string]any)
+	if got := storage["hits"].(float64); got != 20 {
+		t.Errorf("cache.storage.hits: got %v, want 20", got)
+	}
+	if got := storage["misses"].(float64); got != 8 {
+		t.Errorf("cache.storage.misses: got %v, want 8", got)
+	}
+}
+
+// TestBuildSlowBlockLog_EmptyBlock ensures the helper handles a zero-tx,
+// zero-counts block without panic and produces marshalable JSON.
+func TestBuildSlowBlockLog_EmptyBlock(t *testing.T) {
+	stats := &ExecuteStats{}
+	block := fixtureBlock(0, 0)
+	logEntry := buildSlowBlockLog(stats, block)
+	if _, err := json.Marshal(logEntry); err != nil {
+		t.Fatalf("empty block marshal failed: %v", err)
+	}
+	if logEntry.BAL != nil {
+		t.Errorf("empty block should not have bal extension")
+	}
+}