Add WithClock Option

Allow passing current time source.

clock.go

@@ -0,0 +1,16 @@
+package zap
+
+import "time"
+
+// Clock represents time source.
+type Clock interface {
+	// Now returns current time.
+	Now() time.Time
+}
+
+// systemClock implements default Clock that uses system time.
+type systemClock struct{}
+
+func (systemClock) Now() time.Time {
+	return time.Now()
+}

clock_test.go

@@ -0,0 +1,46 @@
+// Copyright (c) 2020 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 zap
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"go.uber.org/zap/zaptest/observer"
+)
+
+type constantClock struct {
+	now time.Time
+}
+
+func (c constantClock) Now() time.Time { return c.now }
+
+func TestWithClock(t *testing.T) {
+	date := time.Date(2077, 1, 23, 10, 15, 13, 441, time.UTC)
+	clock := constantClock{now: date}
+	withLogger(t, DebugLevel, []Option{WithClock(clock)}, func(log *Logger, logs *observer.ObservedLogs) {
+		log.Info("")
+		require.Equal(t, 1, logs.Len(), "Expected only one log entry to be written.")
+		assert.Equal(t, date, logs.All()[0].Entry.Time, "Unexpected entry time.")
+	})
+}

logger.go

@@ -26,7 +26,6 @@ import (
 	"os"
 	"runtime"
 	"strings"
-	"time"
 
 	"go.uber.org/zap/zapcore"
 )
@@ -51,6 +50,8 @@ type Logger struct {
 	addStack zapcore.LevelEnabler
 
 	callerSkip int
+
+	clock Clock
 }
 
 // New constructs a new Logger from the provided zapcore.Core and Options. If
@@ -71,6 +72,7 @@ func New(core zapcore.Core, options ...Option) *Logger {
 		core:        core,
 		errorOutput: zapcore.Lock(os.Stderr),
 		addStack:    zapcore.FatalLevel + 1,
+		clock:       systemClock{},
 	}
 	return log.WithOptions(options...)
 }
@@ -270,7 +272,7 @@ func (log *Logger) check(lvl zapcore.Level, msg string) *zapcore.CheckedEntry {
 	// log message will actually be written somewhere.
 	ent := zapcore.Entry{
 		LoggerName: log.name,
-		Time:       time.Now(),
+		Time:       log.clock.Now(),
 		Level:      lvl,
 		Message:    msg,
 	}
@@ -307,7 +309,7 @@ func (log *Logger) check(lvl zapcore.Level, msg string) *zapcore.CheckedEntry {
 	if log.addCaller {
 		frame, defined := getCallerFrame(log.callerSkip + callerSkipOffset)
 		if !defined {
-			fmt.Fprintf(log.errorOutput, "%v Logger.check error: failed to get caller\n", time.Now().UTC())
+			fmt.Fprintf(log.errorOutput, "%v Logger.check error: failed to get caller\n", log.clock.Now().UTC())
 			log.errorOutput.Sync()
 		}
 

options.go

@@ -22,7 +22,6 @@ package zap
 
 import (
 	"fmt"
-
 	"go.uber.org/zap/zapcore"
 )
 
@@ -138,3 +137,10 @@ func OnFatal(action zapcore.CheckWriteAction) Option {
 		log.onFatal = action
 	})
 }
+
+// WithClock configures the Logger to use Clock while creating entries.
+func WithClock(clock Clock) Option {
+	return optionFunc(func(log *Logger) {
+		log.clock = clock
+	})
+}