add testing logger helper

CHANGELOG.md

@@ -3,6 +3,9 @@ Changelog
 
 ## HEAD
 
+## 1.0.10 2023-08-27
+*   add TestingLogWriter helper bridge to `TB.Log*` 
+
 ## 1.0.9 2023-08-23
 *   fixes
 

flagset_test.go

@@ -1,7 +1,6 @@
 package mlog
 
 import (
-	"fmt"
 	"io"
 	"testing"
 )
@@ -12,7 +11,7 @@ func TestFlagSet(t *testing.T) {
 	expected := Ltimestamp | Ldebug
 	logger.SetFlags(expected)
 	flags := logger.Flags()
-	fmt.Println(flags)
+	t.Log(flags)
 	if flags&(expected) == 0 {
 		t.Errorf("flags did not match\n%12s %#v\n%12s %#v",
 			"expected:", expected.GoString(),

tlogger.go

@@ -0,0 +1,41 @@
+// Copyright (c) 2012-2016 Eli Janssen
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+//
+// some parts from: https://brandur.org/t-parallel
+
+package mlog
+
+import (
+	"fmt"
+	"testing"
+)
+
+// TestoingLogWriter is an adapter between mlog and Go's testing package,
+// which lets us send all output to `t.Log` so that it's correctly
+// collated with the test that emitted it. This helps especially when
+// using parallel testing where output would otherwise be interleaved
+// and make debugging extremely difficult.
+type TestingLogWriter struct {
+	tb testing.TB
+}
+
+func (lw *TestingLogWriter) Write(p []byte) (n int, err error) {
+	// Unfortunately, even with this call to `t.Helper()` there's no
+	// way to correctly attribute the log location to where it's
+	// actually emitted in our code (everything shows up under
+	// `logger.go`). A good explanation of this problem and possible
+	// future solutions here:
+	//
+	// https://github.com/neilotoole/slogt#deficiency
+	if lw == nil {
+		return 0, nil
+	}
+	if lw.tb == nil {
+		fmt.Println("got nil testing.TB")
+		return 0, fmt.Errorf("got a nil testing.TBf")
+	}
+	lw.tb.Helper()
+	lw.tb.Logf(string(p))
+	return len(p), nil
+}

tlogger_test.go

@@ -0,0 +1,12 @@
+package mlog
+
+import (
+	"testing"
+)
+
+func TestTLogger(t *testing.T) {
+	tw := &TestingLogWriter{t}
+	logger := New(tw, 0)
+	logger.Info("test")
+	_ = tw
+}