diff --git a/src/log/slog/level_test.go b/src/log/slog/level_test.go
index 0b28e71e4c..19adcd8466 100644
--- a/src/log/slog/level_test.go
+++ b/src/log/slog/level_test.go
@@ -5,6 +5,7 @@
 package slog
 
 import (
+	"bytes"
 	"flag"
 	"strings"
 	"testing"
@@ -50,12 +51,16 @@ func TestLevelVar(t *testing.T) {
 
 }
 
-func TestMarshalJSON(t *testing.T) {
+func TestLevelMarshalJSON(t *testing.T) {
 	want := LevelWarn - 3
+	wantData := []byte(`"INFO+1"`)
 	data, err := want.MarshalJSON()
 	if err != nil {
 		t.Fatal(err)
 	}
+	if !bytes.Equal(data, wantData) {
+                t.Errorf("got %s, want %s", string(data), string(wantData))
+        }
 	var got Level
 	if err := got.UnmarshalJSON(data); err != nil {
 		t.Fatal(err)
@@ -67,10 +72,14 @@ func TestMarshalJSON(t *testing.T) {
 
 func TestLevelMarshalText(t *testing.T) {
 	want := LevelWarn - 3
+	wantData := []byte("INFO+1")
 	data, err := want.MarshalText()
 	if err != nil {
 		t.Fatal(err)
 	}
+	if !bytes.Equal(data, wantData) {
+                t.Errorf("got %s, want %s", string(data), string(wantData))
+        }
 	var got Level
 	if err := got.UnmarshalText(data); err != nil {
 		t.Fatal(err)