From 4eaa6700face2c2c02779649a148911cd8ffc5c8 Mon Sep 17 00:00:00 2001
From: Michael Schurter <schmichael@hashicorp.com>
Date: Mon, 8 Jan 2018 12:53:58 -0800
Subject: [PATCH] Logger backed by *testing.T

For capturing log output in tests and only displaying them on failure.

Pulled out of #3241
---
 helper/testlog/testlog.go | 40 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)
 create mode 100644 helper/testlog/testlog.go

diff --git a/helper/testlog/testlog.go b/helper/testlog/testlog.go
new file mode 100644
index 000000000..1b18bc025
--- /dev/null
+++ b/helper/testlog/testlog.go
@@ -0,0 +1,40 @@
+// Package testlog creates a *log.Logger backed by testing.T to ease logging in
+// tests.
+package testlog
+
+import (
+	"io"
+	"log"
+)
+
+// Logger is the methods of testing.T (or testing.B) needed by the test
+// logger.
+type Logger interface {
+	Logf(format string, args ...interface{})
+}
+
+// writer implements io.Writer on top of a Logger.
+type writer struct {
+	t Logger
+}
+
+// Write to an underlying Logger. Never returns an error.
+func (w *writer) Write(p []byte) (n int, err error) {
+	w.t.Logf(string(p))
+	return len(p), nil
+}
+
+// NewWriter creates a new io.Writer backed by a Logger.
+func NewWriter(t Logger) io.Writer {
+	return &writer{t}
+}
+
+// NewLog returns a new test logger. See https://golang.org/pkg/log/#New
+func NewLog(t Logger, prefix string, flag int) *log.Logger {
+	return log.New(&writer{t}, prefix, flag)
+}
+
+// New logger with "TEST" prefix and the Lmicroseconds flag.
+func New(t Logger) *log.Logger {
+	return NewLog(t, "TEST ", log.Lmicroseconds)
+}