log/slog: test built-in handlers with slogtest

Test the built-in handlers using the testing/slogtest package.

Change-Id: I6464b6730293461c38b84fb2bf33cdd09173dd6e
Reviewed-on: https://go-review.googlesource.com/c/go/+/488255
Run-TryBot: Jonathan Amsterdam <jba@google.com>
Reviewed-by: Alan Donovan <adonovan@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

src/log/slog/slogtest_test.go

@@ -0,0 +1,104 @@
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package slog_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"strings"
+	"testing"
+	"testing/slogtest"
+)
+
+func TestSlogtest(t *testing.T) {
+	for _, test := range []struct {
+		name  string
+		new   func(io.Writer) slog.Handler
+		parse func([]byte) (map[string]any, error)
+	}{
+		{"JSON", func(w io.Writer) slog.Handler { return slog.NewJSONHandler(w, nil) }, parseJSON},
+		{"Text", func(w io.Writer) slog.Handler { return slog.NewTextHandler(w, nil) }, parseText},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			var buf bytes.Buffer
+			h := test.new(&buf)
+			results := func() []map[string]any {
+				ms, err := parseLines(buf.Bytes(), test.parse)
+				if err != nil {
+					t.Fatal(err)
+				}
+				return ms
+			}
+			if err := slogtest.TestHandler(h, results); err != nil {
+				t.Fatal(err)
+			}
+		})
+	}
+}
+
+func parseLines(src []byte, parse func([]byte) (map[string]any, error)) ([]map[string]any, error) {
+	var records []map[string]any
+	for _, line := range bytes.Split(src, []byte{'\n'}) {
+		if len(line) == 0 {
+			continue
+		}
+		m, err := parse(line)
+		if err != nil {
+			return nil, fmt.Errorf("%s: %w", string(line), err)
+		}
+		records = append(records, m)
+	}
+	return records, nil
+}
+
+func parseJSON(bs []byte) (map[string]any, error) {
+	var m map[string]any
+	if err := json.Unmarshal(bs, &m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// parseText parses the output of a single call to TextHandler.Handle.
+// It can parse the output of the tests in this package,
+// but it doesn't handle quoted keys or values.
+// It doesn't need to handle all cases, because slogtest deliberately
+// uses simple inputs so handler writers can focus on testing
+// handler behavior, not parsing.
+func parseText(bs []byte) (map[string]any, error) {
+	top := map[string]any{}
+	s := string(bytes.TrimSpace(bs))
+	for len(s) > 0 {
+		kv, rest, _ := strings.Cut(s, " ") // assumes exactly one space between attrs
+		k, value, found := strings.Cut(kv, "=")
+		if !found {
+			return nil, fmt.Errorf("no '=' in %q", kv)
+		}
+		keys := strings.Split(k, ".")
+		// Populate a tree of maps for a dotted path such as "a.b.c=x".
+		m := top
+		for _, key := range keys[:len(keys)-1] {
+			x, ok := m[key]
+			var m2 map[string]any
+			if !ok {
+				m2 = map[string]any{}
+				m[key] = m2
+			} else {
+				m2, ok = x.(map[string]any)
+				if !ok {
+					return nil, fmt.Errorf("value for %q in composite key %q is not map[string]any", key, k)
+
+				}
+			}
+			m = m2
+		}
+		m[keys[len(keys)-1]] = value
+		s = rest
+	}
+	return top, nil
+}