logtest: Add Recorder (#5134)

* introduce in-memory log exporter

* add changelog entry

* move logtest into a recorder within the api

* rename GetRecords to Result

* rename InMemoryRecorder to Recorder

* name the struct r

* ensure Logger creates a struct copy

* replace severity with enabledFn

* Update CHANGELOG.md

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* kUpdate log/logtest/config.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* store all scope records, so we can retrieve everything with `Result()`

* store child loggers instead of all scope records

* no need to explicitly create a new slice

* add concurrent safe test

* handle default enabled function if the struct was manually created

* rename WithEnabledFn to WithEnabledFunc

* test result/reset with child loggers

* add enabled to concurrent safe

* fix lint missing period

* rename defaultEnabledFn to defaultEnabledFunc

* merge recorder.go and config.go

* Update log/logtest/recorder_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* create empty recorder in concurrent safe test

* Update log/logtest/recorder_test.go

Co-authored-by: Robert Pająk <pellared@hotmail.com>

* fix lint

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* Update log/logtest/recorder.go

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

* make enabledFunc callable from outside the package

* replace expected with want

---------

Co-authored-by: Robert Pająk <pellared@hotmail.com>
Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>
Co-authored-by: Sam Xie <sam@samxie.me>

CHANGELOG.md

@@ -29,6 +29,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
 - Add `String` method to `Value` and `KeyValue` in `go.opentelemetry.io/otel/log`. (#5117)
 - Add Exemplar support to `go.opentelemetry.io/otel/exporters/prometheus`. (#5111)
 - Add metric semantic conventions to `go.opentelemetry.io/otel/semconv/v1.24.0`. Future `semconv` packages will include metric semantic conventions as well. (#4528)
+- Add `Recorder` in `go.opentelemetry.io/otel/log/logtest` to facilitate testing the log bridge implementations. (#5134)
 
 ### Changed
 

log/logtest/README.md

@@ -0,0 +1,3 @@
+# Log Test
+
+[![PkgGoDev](https://pkg.go.dev/badge/go.opentelemetry.io/otel/log/logtest)](https://pkg.go.dev/go.opentelemetry.io/otel/log/logtest)

log/logtest/recorder.go

@@ -0,0 +1,164 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+// Package logtest is a testing helper package. Users can retrieve an in-memory
+// logger to verify the behavior of their integrations.
+package logtest // import "go.opentelemetry.io/otel/log/logtest"
+
+import (
+	"context"
+	"sync"
+
+	"go.opentelemetry.io/otel/log"
+	"go.opentelemetry.io/otel/log/embedded"
+)
+
+// embeddedLogger is a type alias so the embedded.Logger type doesn't conflict
+// with the Logger method of the Recorder when it is embedded.
+type embeddedLogger = embedded.Logger // nolint:unused  // Used below.
+
+type enabledFn func(context.Context, log.Record) bool
+
+var defaultEnabledFunc = func(context.Context, log.Record) bool {
+	return true
+}
+
+type config struct {
+	enabledFn enabledFn
+}
+
+func newConfig(options []Option) config {
+	var c config
+	for _, opt := range options {
+		c = opt.apply(c)
+	}
+
+	return c
+}
+
+// Option configures a [Recorder].
+type Option interface {
+	apply(config) config
+}
+
+type optFunc func(config) config
+
+func (f optFunc) apply(c config) config { return f(c) }
+
+// WithEnabledFunc allows configuring whether the [Recorder] is enabled for specific log entries or not.
+//
+// By default, the Recorder is enabled for every log entry.
+func WithEnabledFunc(fn func(context.Context, log.Record) bool) Option {
+	return optFunc(func(c config) config {
+		c.enabledFn = fn
+		return c
+	})
+}
+
+// NewRecorder returns a new [Recorder].
+func NewRecorder(options ...Option) *Recorder {
+	cfg := newConfig(options)
+
+	sr := &ScopeRecords{}
+
+	return &Recorder{
+		currentScopeRecord: sr,
+		enabledFn:          cfg.enabledFn,
+	}
+}
+
+// ScopeRecords represents the records for a single instrumentation scope.
+type ScopeRecords struct {
+	// Name is the name of the instrumentation scope.
+	Name string
+	// Version is the version of the instrumentation scope.
+	Version string
+	// SchemaURL of the telemetry emitted by the scope.
+	SchemaURL string
+
+	// Records are the log records this instrumentation scope recorded.
+	Records []log.Record
+}
+
+// Recorder is a recorder that stores all received log records
+// in-memory.
+type Recorder struct {
+	embedded.LoggerProvider
+	embeddedLogger // nolint:unused  // Used to embed embedded.Logger.
+
+	mu sync.Mutex
+
+	loggers            []*Recorder
+	currentScopeRecord *ScopeRecords
+
+	// enabledFn decides whether the recorder should enable logging of a record or not
+	enabledFn enabledFn
+}
+
+// Logger returns a copy of Recorder as a [log.Logger] with the provided scope
+// information.
+func (r *Recorder) Logger(name string, opts ...log.LoggerOption) log.Logger {
+	cfg := log.NewLoggerConfig(opts...)
+
+	nr := &Recorder{
+		currentScopeRecord: &ScopeRecords{
+			Name:      name,
+			Version:   cfg.InstrumentationVersion(),
+			SchemaURL: cfg.SchemaURL(),
+		},
+		enabledFn: r.enabledFn,
+	}
+	r.addChildLogger(nr)
+
+	return nr
+}
+
+func (r *Recorder) addChildLogger(nr *Recorder) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	r.loggers = append(r.loggers, nr)
+}
+
+// Enabled indicates whether a specific record should be stored.
+func (r *Recorder) Enabled(ctx context.Context, record log.Record) bool {
+	if r.enabledFn == nil {
+		return defaultEnabledFunc(ctx, record)
+	}
+
+	return r.enabledFn(ctx, record)
+}
+
+// Emit stores the log record.
+func (r *Recorder) Emit(_ context.Context, record log.Record) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	r.currentScopeRecord.Records = append(r.currentScopeRecord.Records, record)
+}
+
+// Result returns the current in-memory recorder log records.
+func (r *Recorder) Result() []*ScopeRecords {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	ret := []*ScopeRecords{}
+	ret = append(ret, r.currentScopeRecord)
+	for _, l := range r.loggers {
+		ret = append(ret, l.Result()...)
+	}
+	return ret
+}
+
+// Reset clears the in-memory log records.
+func (r *Recorder) Reset() {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	if r.currentScopeRecord != nil {
+		r.currentScopeRecord.Records = nil
+	}
+	for _, l := range r.loggers {
+		l.Reset()
+	}
+}

log/logtest/recorder_test.go

@@ -0,0 +1,156 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package logtest
+
+import (
+	"context"
+	"sync"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"go.opentelemetry.io/otel/log"
+)
+
+func TestRecorderLogger(t *testing.T) {
+	for _, tt := range []struct {
+		name    string
+		options []Option
+
+		loggerName    string
+		loggerOptions []log.LoggerOption
+
+		wantLogger log.Logger
+	}{
+		{
+			name: "provides a default logger",
+
+			wantLogger: &Recorder{
+				currentScopeRecord: &ScopeRecords{},
+			},
+		},
+		{
+			name: "provides a logger with a configured scope",
+
+			loggerName: "test",
+			loggerOptions: []log.LoggerOption{
+				log.WithInstrumentationVersion("logtest v42"),
+				log.WithSchemaURL("https://example.com"),
+			},
+
+			wantLogger: &Recorder{
+				currentScopeRecord: &ScopeRecords{
+					Name:      "test",
+					Version:   "logtest v42",
+					SchemaURL: "https://example.com",
+				},
+			},
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			l := NewRecorder(tt.options...).Logger(tt.loggerName, tt.loggerOptions...)
+			// unset enabledFn to allow comparison
+			l.(*Recorder).enabledFn = nil
+
+			assert.Equal(t, tt.wantLogger, l)
+		})
+	}
+}
+
+func TestRecorderLoggerCreatesNewStruct(t *testing.T) {
+	r := &Recorder{}
+	assert.NotEqual(t, r, r.Logger("test"))
+}
+
+func TestRecorderEnabled(t *testing.T) {
+	for _, tt := range []struct {
+		name        string
+		options     []Option
+		ctx         context.Context
+		buildRecord func() log.Record
+
+		isEnabled bool
+	}{
+		{
+			name: "the default option enables every log entry",
+			ctx:  context.Background(),
+			buildRecord: func() log.Record {
+				return log.Record{}
+			},
+
+			isEnabled: true,
+		},
+		{
+			name: "with everything disabled",
+			options: []Option{
+				WithEnabledFunc(func(context.Context, log.Record) bool {
+					return false
+				}),
+			},
+			ctx: context.Background(),
+			buildRecord: func() log.Record {
+				return log.Record{}
+			},
+
+			isEnabled: false,
+		},
+	} {
+		t.Run(tt.name, func(t *testing.T) {
+			e := NewRecorder(tt.options...).Enabled(tt.ctx, tt.buildRecord())
+			assert.Equal(t, tt.isEnabled, e)
+		})
+	}
+}
+
+func TestRecorderEnabledFnUnset(t *testing.T) {
+	r := &Recorder{}
+	assert.True(t, r.Enabled(context.Background(), log.Record{}))
+}
+
+func TestRecorderEmitAndReset(t *testing.T) {
+	r := NewRecorder()
+	assert.Len(t, r.Result()[0].Records, 0)
+
+	r1 := log.Record{}
+	r1.SetSeverity(log.SeverityInfo)
+	r.Emit(context.Background(), r1)
+	assert.Equal(t, r.Result()[0].Records, []log.Record{r1})
+
+	l := r.Logger("test")
+	assert.Empty(t, r.Result()[1].Records)
+
+	r2 := log.Record{}
+	r2.SetSeverity(log.SeverityError)
+	l.Emit(context.Background(), r2)
+	assert.Equal(t, r.Result()[0].Records, []log.Record{r1})
+	assert.Equal(t, r.Result()[1].Records, []log.Record{r2})
+
+	r.Reset()
+	assert.Empty(t, r.Result()[0].Records)
+	assert.Empty(t, r.Result()[1].Records)
+}
+
+func TestRecorderConcurrentSafe(t *testing.T) {
+	const goRoutineN = 10
+
+	var wg sync.WaitGroup
+	wg.Add(goRoutineN)
+
+	r := &Recorder{}
+
+	for i := 0; i < goRoutineN; i++ {
+		go func() {
+			defer wg.Done()
+
+			nr := r.Logger("test")
+			nr.Enabled(context.Background(), log.Record{})
+			nr.Emit(context.Background(), log.Record{})
+
+			r.Result()
+			r.Reset()
+		}()
+	}
+
+	wg.Wait()
+}