zaptest: Add testing.TB compatible logger

This adds `zaptest.NewTestLogger(testing.TB) *zap.Logger` and a
level-override variant of it. This will enable us to use non-nop loggers
from tests without spamming the output.

These loggers will not print any output unless the test failed or
`go test -v` was used.

zaptest/test_logger.go

@@ -0,0 +1,86 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zaptest
+
+import (
+	"testing"
+
+	"go.uber.org/zap/zapcore"
+)
+
+// NewTestLogger builds a new Core that logs all messages to the given
+// testing.TB.
+//
+// Use this with a *testing.T or *testing.B to get logs which get printed only
+// if a test fails or if you ran go test -v.
+//
+//   logger := zap.New(NewTestLogger(t))
+func NewTestLogger(t testing.TB) zapcore.Core {
+	return NewTestLoggerAt(t, zapcore.DebugLevel)
+}
+
+// NewTestLoggerAt builds a new Core that logs messages to the given
+// testing.TB if the given LevelEnabler allows it.
+//
+// Use this with a *testing.T or *testing.B to get logs which get printed only
+// if a test fails or if you ran go test -v.
+//
+//   logger := zap.New(NewTestLoggerAt(t, zap.InfoLevel))
+func NewTestLoggerAt(t testing.TB, enab zapcore.LevelEnabler) zapcore.Core {
+	return zapcore.NewCore(
+		zapcore.NewConsoleEncoder(zapcore.EncoderConfig{
+			// EncoderConfig copied from zap.NewDevelopmentEncoderConfig.
+			TimeKey:        "T",
+			LevelKey:       "L",
+			NameKey:        "N",
+			CallerKey:      "C",
+			MessageKey:     "M",
+			StacktraceKey:  "S",
+			LineEnding:     zapcore.DefaultLineEnding,
+			EncodeLevel:    zapcore.CapitalLevelEncoder,
+			EncodeTime:     zapcore.ISO8601TimeEncoder,
+			EncodeDuration: zapcore.StringDurationEncoder,
+			EncodeCaller:   zapcore.ShortCallerEncoder,
+		}),
+		testingWriter{t},
+		enab,
+	)
+}
+
+// testingWriter is a WriteSyncer that writes to the given testing.TB.
+type testingWriter struct{ t testing.TB }
+
+func (w testingWriter) Write(p []byte) (n int, err error) {
+	s := string(p)
+
+	// Strip trailing newline because t.Log always adds one.
+	if s[len(s)-1] == '\n' {
+		s = s[:len(s)-1]
+	}
+
+	// Note: t.Log is safe for concurrent use.
+	w.t.Log(s)
+	return len(p), nil
+}
+
+func (w testingWriter) Sync() error {
+	return nil
+}

zaptest/test_logger_test.go

@@ -0,0 +1,99 @@
+// Copyright (c) 2017 Uber Technologies, Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package zaptest
+
+import (
+	"errors"
+	"fmt"
+	"strings"
+	"sync"
+	"testing"
+
+	"go.uber.org/zap"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTestLoggerIncludesDebug(t *testing.T) {
+	ts := newTestLogSpy(t)
+	log := zap.New(NewTestLogger(ts))
+	log.Debug("calculating")
+	log.Info("finished calculating", zap.Int("answer", 42))
+
+	ts.AssertMessages(
+		"DEBUG	calculating",
+		`INFO	finished calculating	{"answer": 42}`,
+	)
+}
+
+func TestTestLoggerAt(t *testing.T) {
+	ts := newTestLogSpy(t)
+	log := zap.New(NewTestLoggerAt(ts, zap.WarnLevel))
+
+	log.Info("received work order")
+	log.Debug("starting work")
+	log.Warn("work may fail")
+	log.Error("work failed", zap.Error(errors.New("great sadness")))
+
+	assert.Panics(t, func() {
+		log.Panic("failed to do work")
+	}, "log.Panic should panic")
+
+	ts.AssertMessages(
+		"WARN	work may fail",
+		`ERROR	work failed	{"error": "great sadness"}`,
+		"PANIC	failed to do work",
+	)
+}
+
+// testLogSpy is a testing.TB that captures logged messages.
+type testLogSpy struct {
+	testing.TB
+
+	mu       sync.Mutex
+	Messages []string
+}
+
+func newTestLogSpy(t testing.TB) *testLogSpy {
+	return &testLogSpy{TB: t}
+}
+
+func (t *testLogSpy) Log(args ...interface{}) {
+	// Log messages are in the format,
+	//
+	//   2017-10-27T13:03:01.000-0700	DEBUG	your message here	{data here}
+	//
+	// We strip the first part of these messages because we can't really test
+	// for the timestamp from these tests.
+	m := fmt.Sprint(args...)
+	m = m[strings.IndexByte(m, '\t')+1:]
+
+	// t.Log should be thread-safe.
+	t.mu.Lock()
+	t.Messages = append(t.Messages, m)
+	t.mu.Unlock()
+
+	t.TB.Log(args...)
+}
+
+func (t *testLogSpy) AssertMessages(msgs ...string) {
+	assert.Equal(t, msgs, t.Messages)
+}