[logp] Default logging config logs to file

The default log configuration must log to files. A test is added to
ensure the default logging configuration logs to files as well as some
other default fields are correctly set.

logp/config.go

@@ -71,7 +71,8 @@ const (
 // Beat is supposed to be run within.
 func DefaultConfig(environment Environment) Config {
 	return Config{
-		Level: defaultLevel,
+		Level:   defaultLevel,
+		ToFiles: true,
 		Files: FileConfig{
 			MaxSize:         10 * 1024 * 1024,
 			MaxBackups:      7,

logp/defaults_test.go

@@ -0,0 +1,92 @@
+package logp_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+
+	"github.com/elastic/elastic-agent-libs/logp"
+)
+
+// TestDefaultConfig tests the default config ensuring the default
+// behaviour is to log to files
+func TestDefaultConfig(t *testing.T) {
+	cfg := logp.DefaultConfig(logp.DefaultEnvironment)
+
+	// Set cfg.Beat to avoid a log file like '-202405029.ndjson'
+	cfg.Beat = t.Name()
+
+	// Set Files.Path to an empty folder so we can assert the
+	// creation of the log file without being affected by other
+	// test runs.
+	cfg.Files.Path = t.TempDir()
+
+	if err := logp.Configure(cfg); err != nil {
+		t.Fatalf("did not expect an error calling logp.Configure: %s", err)
+	}
+
+	// Get the logger and log anything
+	logger := logp.L()
+	logger.Info("foo")
+	_, fileName, lineNum, _ := runtime.Caller(0)
+	lineNum-- // We want the line number from the log
+	fileName = filepath.Base(fileName)
+
+	// Assert the log file was created
+	glob := fmt.Sprintf("%s-*.ndjson", t.Name())
+	glob = filepath.Join(cfg.Files.Path, glob)
+	logFiles, err := filepath.Glob(glob)
+	if err != nil {
+		t.Fatalf("could not list files for glob '%s', err: %s", glob, err)
+	}
+
+	if len(logFiles) < 1 {
+		t.Fatalf("did not find any log file")
+	}
+
+	data, err := os.ReadFile(logFiles[0])
+	if err != nil {
+		t.Fatalf("cannot open file '%s', err: %s", logFiles[0], err)
+	}
+
+	logEntry := struct {
+		LogLevel  string `json:"log.level"`
+		LogOrigin struct {
+			FileName string `json:"file.name"`
+			FileLine int    `json:"file.line"`
+		} `json:"log.origin"`
+		Message     string `json:"message"`
+		ServiceName string `json:"service.name"`
+	}{}
+	if err := json.Unmarshal(data, &logEntry); err != nil {
+		t.Fatalf("cannot unmarshal log entry: %s", err)
+	}
+
+	if got, expect := logEntry.Message, "foo"; got != expect {
+		t.Errorf("expecting message '%s', got '%s'", expect, got)
+	}
+
+	if got, expect := logEntry.LogLevel, "info"; got != expect {
+		t.Errorf("expecting level '%s', got '%s'", expect, got)
+	}
+
+	if got, expect := logEntry.ServiceName, t.Name(); got != expect {
+		t.Errorf("expecting service name '%s', got '%s'", expect, got)
+	}
+
+	if got, expect := filepath.Base(logEntry.LogOrigin.FileName), fileName; got != expect {
+		t.Errorf("expecting log.origin.file.name '%s', got '%s'", expect, got)
+	}
+
+	if got, expect := logEntry.LogOrigin.FileLine, lineNum; got != expect {
+		t.Errorf("expecting log.origin.file.line '%d', got '%d'", expect, got)
+	}
+
+	if t.Failed() {
+		t.Log("Original log entry:")
+		t.Log(string(data))
+	}
+}