test: add comprehensive benchmark suite

Adds benchmarks for all log levels (Trace, Debug, Info, Warn, Error),
formatted logging, multiple client fan-out, parallel writes, namespace
filtering, and component-level benchmarks (fileInfo, entry creation).

Uses isolated namespaces to avoid interference with the stderr client.

Fixes #6

.github/workflows/ci.yaml

@@ -11,7 +11,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v4
         with:
-          go-version: "1.21"
+          go-version: "1.25"
 
       - name: Install dependencies
         run: go get .

log/bench_test.go

@@ -0,0 +1,171 @@
+package log
+
+import (
+	"fmt"
+	"testing"
+)
+
+const benchNS = "bench-isolated-ns"
+
+// benchClient creates a client with a continuous drain goroutine.
+// Returns the client and a stop function to call after b.StopTimer().
+func benchClient(ns string) (*Client, func()) {
+	c := CreateClient(ns)
+	c.SetLogLevel(LTrace)
+	done := make(chan struct{})
+	go func() {
+		for {
+			select {
+			case <-done:
+				return
+			case <-c.writer:
+			}
+		}
+	}()
+	return c, func() {
+		close(done)
+		c.Destroy()
+	}
+}
+
+// BenchmarkCreateClient measures client creation overhead.
+func BenchmarkCreateClient(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		c := CreateClient("bench")
+		c.Destroy()
+	}
+}
+
+// BenchmarkTrace benchmarks Logger.Trace.
+func BenchmarkTrace(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Trace("benchmark trace message")
+	}
+}
+
+// BenchmarkTracef benchmarks formatted Logger.Tracef.
+func BenchmarkTracef(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Tracef("benchmark trace message %d", i)
+	}
+}
+
+// BenchmarkDebug benchmarks Logger.Debug.
+func BenchmarkDebug(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Debug("benchmark debug message")
+	}
+}
+
+// BenchmarkInfo benchmarks Logger.Info.
+func BenchmarkInfo(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Info("benchmark info message")
+	}
+}
+
+// BenchmarkInfof benchmarks Logger.Infof with formatting.
+func BenchmarkInfof(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Infof("user %s performed action %d", "testuser", i)
+	}
+}
+
+// BenchmarkWarn benchmarks Logger.Warn.
+func BenchmarkWarn(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Warn("benchmark warn message")
+	}
+}
+
+// BenchmarkError benchmarks Logger.Error.
+func BenchmarkError(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Error("benchmark error message")
+	}
+}
+
+// BenchmarkMultipleClients measures fan-out to multiple consumers.
+func BenchmarkMultipleClients(b *testing.B) {
+	const numClients = 5
+	l := NewLogger(benchNS)
+	stops := make([]func(), numClients)
+	for i := range stops {
+		_, stops[i] = benchClient(benchNS)
+	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Info("benchmark multi-client")
+	}
+	b.StopTimer()
+	for _, stop := range stops {
+		stop()
+	}
+}
+
+// BenchmarkParallelInfo benchmarks concurrent Info calls from multiple goroutines.
+func BenchmarkParallelInfo(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient(benchNS)
+	defer stop()
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			l.Info("parallel benchmark info")
+		}
+	})
+}
+
+// BenchmarkNamespaceFiltering benchmarks logging when the consumer
+// filters by a different namespace (messages are not delivered).
+func BenchmarkNamespaceFiltering(b *testing.B) {
+	l := NewLogger(benchNS)
+	_, stop := benchClient("completely-different-ns")
+	defer stop()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		l.Info("filtered out message")
+	}
+}
+
+// BenchmarkFileInfo measures the cost of runtime.Caller for file info.
+func BenchmarkFileInfo(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		fileInfo(1)
+	}
+}
+
+// BenchmarkEntryCreation measures raw fmt.Sprint overhead (baseline).
+func BenchmarkEntryCreation(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		_ = fmt.Sprint("benchmark message ", i)
+	}
+}