[chore] [receiver/filelog] test: add benchmark for File Log receiver (#38171)

#### Description

Related to
#38054.

The File Log receiver benchmark has a scope that is larger than both the
[File consumer
benchmark](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/fileconsumer/benchmark_test.go)
and the [File input
benchmark](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/operator/input/file/benchmark_test.go).
Compared to the File input benchmark, the scope of File Log receiver
benchmark includes:
- translating of Stanza entries to pdata logs
([converter.ConvertEntries](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/adapter/converter.go#L20)).
- batching of logs in
[LogEmitter](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/a826350bab9388e7ab8179f1e02c68177d83f0b4/pkg/stanza/operator/helper/emitter.go#L103).

This new benchmark should help us measure the performance impact of
[removing batching from
LogEmitter](#35456)
after it is [added in File
consumer](#35455).

#### Link to tracking issue

- Needed for
#35456

Author: andrzej-stencel

receiver/filelogreceiver/benchmark_test.go

@@ -0,0 +1,59 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package filelogreceiver
+
+import (
+	"context"
+	"fmt"
+	"math"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+	"go.opentelemetry.io/collector/component/componenttest"
+	"go.opentelemetry.io/collector/consumer/consumertest"
+	"go.opentelemetry.io/collector/receiver/receivertest"
+
+	"github.com/open-telemetry/opentelemetry-collector-contrib/pkg/stanza/operator/input/file"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/receiver/filelogreceiver/internal/metadata"
+	"github.com/open-telemetry/opentelemetry-collector-contrib/receiver/filelogreceiver/internal/testutil"
+)
+
+func BenchmarkReadSingleStaticFile(b *testing.B) {
+	for n := range 6 {
+		numLines := int(math.Pow(10, float64(n)))
+		b.Run(fmt.Sprintf("%d-lines", numLines), func(b *testing.B) {
+			benchmarkReadSingleStaticFile(b, numLines)
+		})
+	}
+}
+
+func benchmarkReadSingleStaticFile(b *testing.B, numLines int) {
+	logFileGenerator := testutil.NewLogFileGenerator(b)
+	logFilePath := logFileGenerator.GenerateLogFile(numLines)
+
+	cfg := &FileLogConfig{
+		InputConfig: func() file.Config {
+			c := file.NewConfig()
+			c.Include = []string{logFilePath}
+			c.PollInterval = time.Microsecond
+			c.StartAt = "beginning"
+			return *c
+		}(),
+	}
+	sink := new(consumertest.LogsSink)
+	f := NewFactory()
+
+	b.ResetTimer()
+	for range b.N {
+		rcvr, err := f.CreateLogs(context.Background(), receivertest.NewNopSettings(metadata.Type), cfg, sink)
+		require.NoError(b, err)
+		require.NoError(b, rcvr.Start(context.Background(), componenttest.NewNopHost()))
+
+		require.Eventually(b, expectNLogs(sink, numLines), 2*time.Second, 2*time.Microsecond)
+		sink.Reset()
+
+		require.NoError(b, rcvr.Shutdown(context.Background()))
+	}
+}

receiver/filelogreceiver/internal/testutil/log_file_generator.go

@@ -0,0 +1,51 @@
+// Copyright The OpenTelemetry Authors
+// SPDX-License-Identifier: Apache-2.0
+
+package testutil // import "github.com/open-telemetry/opentelemetry-collector-contrib/receiver/filelogreceiver/internal/testutil"
+
+import (
+	"math/rand/v2"
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type LogFileGenerator struct {
+	tb       testing.TB
+	charset  []byte
+	logLines [][]byte
+}
+
+func NewLogFileGenerator(tb testing.TB) *LogFileGenerator {
+	logFileGenerator := &LogFileGenerator{
+		tb:      tb,
+		charset: []byte("abcdefghijklmnopqrstuvwxyz"),
+	}
+	logFileGenerator.logLines = logFileGenerator.generateLogLines(8, 999)
+	return logFileGenerator
+}
+
+func (g *LogFileGenerator) generateLogLines(numLines, lineLength int) (logLines [][]byte) {
+	logLines = make([][]byte, numLines)
+	for i := range numLines {
+		logLines[i] = make([]byte, lineLength)
+		for j := range lineLength {
+			logLines[i][j] = g.charset[rand.IntN(len(g.charset))]
+		}
+	}
+	return logLines
+}
+
+func (g *LogFileGenerator) GenerateLogFile(numLines int) (logFilePath string) {
+	f, err := os.CreateTemp(g.tb.TempDir(), "")
+	require.NoError(g.tb, err)
+	g.tb.Cleanup(func() { _ = f.Close() })
+	for range numLines {
+		_, err := f.Write(g.logLines[rand.IntN(len(g.logLines))])
+		require.NoError(g.tb, err)
+		_, err = f.WriteString("\n")
+		require.NoError(g.tb, err)
+	}
+	return f.Name()
+}