zapslog: Test with slogtest

Adds a test for zapslog that verifies its behavior
with slogtest's TestHandler function.
This verifies compliance with the slog logging contract.

Resolves uber-go#1334

exp/zapslog/handler_test.go

@@ -23,13 +23,17 @@
 package zapslog
 
 import (
+	"bytes"
+	"encoding/json"
 	"log/slog"
 	"testing"
+	"testing/slogtest"
 	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.uber.org/zap/zapcore"
+	"go.uber.org/zap/zaptest"
 	"go.uber.org/zap/zaptest/observer"
 )
 
@@ -189,3 +193,41 @@ func TestAttrKinds(t *testing.T) {
 		},
 		entry.ContextMap())
 }
+
+func TestSlogtest(t *testing.T) {
+	var buff bytes.Buffer
+	core := zapcore.NewCore(
+		zapcore.NewJSONEncoder(zapcore.EncoderConfig{
+			TimeKey:     slog.TimeKey,
+			MessageKey:  slog.MessageKey,
+			LevelKey:    slog.LevelKey,
+			EncodeLevel: zapcore.CapitalLevelEncoder,
+			EncodeTime:  zapcore.RFC3339TimeEncoder,
+		}),
+		zapcore.AddSync(&buff),
+		zapcore.DebugLevel,
+	)
+
+	// zaptest doesn't expose the underlying core,
+	// so we'll extract it from the logger.
+	testCore := zaptest.NewLogger(t).Core()
+
+	handler := NewHandler(zapcore.NewTee(core, testCore))
+	err := slogtest.TestHandler(
+		handler,
+		func() []map[string]any {
+			// Parse the newline-delimted JSON in buff.
+			var entries []map[string]any
+
+			dec := json.NewDecoder(bytes.NewReader(buff.Bytes()))
+			for dec.More() {
+				var ent map[string]any
+				require.NoError(t, dec.Decode(&ent), "Error decoding log message")
+				entries = append(entries, ent)
+			}
+
+			return entries
+		},
+	)
+	require.NoError(t, err, "Unexpected error from slogtest.TestHandler")
+}