internal/testlog: add logger for unit tests

internal/testlog/testlog.go

+// Copyright 2017 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+// Package testlog provides a log handler for unit tests.
+package testlog
+
+import (
+	"testing"
+
+	"github.com/ethereum/go-ethereum/log"
+)
+
+// Logger returns a logger which logs to the unit test log of t.
+func Logger(t *testing.T, level log.Lvl) log.Logger {
+	l := log.New()
+	l.SetHandler(Handler(t, level))
+	return l
+}
+
+// Handler returns a log handler which logs to the unit test log of t.
+func Handler(t *testing.T, level log.Lvl) log.Handler {
+	return log.LvlFilterHandler(level, &handler{t, log.TerminalFormat(false)})
+}
+
+type handler struct {
+	t   *testing.T
+	fmt log.Format
+}
+
+func (h *handler) Log(r *log.Record) error {
+	h.t.Logf("%s", h.fmt.Format(r))
+	return nil
+}