Merge pull request #3729 from hashicorp/f-test-log-2

Logger backed by *testing.T

helper/testlog/testlog.go

@@ -0,0 +1,46 @@
+// Package testlog creates a *log.Logger backed by *testing.T to ease logging
+// in tests. This allows logs from components being tested to only be printed
+// if the test fails (or the verbose flag is specified).
+package testlog
+
+import (
+	"io"
+	"log"
+)
+
+// LogPrinter is the methods of testing.T (or testing.B) needed by the test
+// logger.
+type LogPrinter interface {
+	Logf(format string, args ...interface{})
+}
+
+// writer implements io.Writer on top of a Logger.
+type writer struct {
+	t LogPrinter
+}
+
+// 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 LogPrinter) io.Writer {
+	return &writer{t}
+}
+
+// New returns a new test logger. See https://golang.org/pkg/log/#New
+func New(t LogPrinter, prefix string, flag int) *log.Logger {
+	return log.New(&writer{t}, prefix, flag)
+}
+
+// WithPrefix returns a new test logger with the Lmicroseconds flag set.
+func WithPrefix(t LogPrinter, prefix string) *log.Logger {
+	return New(t, prefix, log.Lmicroseconds)
+}
+
+// NewLog logger with "TEST" prefix and the Lmicroseconds flag.
+func Logger(t LogPrinter) *log.Logger {
+	return WithPrefix(t, "TEST ")
+}