You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: buffered_write_syncer_test.go
    path of file: ./repos/zap/zapcore
    
    the code of the file until where you have to start completion: // Copyright (c) 2021 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 zapcore

import (
	"bytes"
	"testing"
	"time"

	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"go.uber.org/zap/internal/ztest"
)

func TestBufferWriter(t *testing.T) {
	// If we pass a plain io.Writer, make sure that we still get a WriteSyncer
	// with a no-op Sync.
	t.Run("sync", func(t *testing.T) {
		buf := &bytes.Buffer{}
		ws := &BufferedWrit
    
func TestBufferWriter(t *testing.T) {
	// If we pass a plain io.Writer, make sure that we still get a WriteSyncer
	// with a no-op Sync.
	t.Run("sync", func(t *testing.T) {
		buf := &bytes.Buffer{}
		ws := &BufferedWriteSyncer{WS: AddSync(buf)}

		requireWriteWorks(t, ws)
		assert.Empty(t, buf.String(), "Unexpected log calling a no-op Write method.")
		assert.NoError(t, ws.Sync(), "Unexpected error calling a no-op Sync method.")
		assert.Equal(t, "foo", buf.String(), "Unexpected log string")
		assert.NoError(t, ws.Stop())
	})

	t.Run("stop", func(t *testing.T) {
		buf := &bytes.Buffer{}
		ws := &BufferedWriteSyncer{WS: AddSync(buf)}
		requireWriteWorks(t, ws)
		assert.Empty(t, buf.String(), "Unexpected log calling a no-op Write method.")
		assert.NoError(t, ws.Stop())
		assert.Equal(t, "foo", buf.String(), "Unexpected log string")
	})

	t.Run("stop twice", func(t *testing.T) {
		ws := &BufferedWriteSyncer{WS: &ztest.FailWriter{}}
		_, err := ws.Write([]byte("foo"))
		require.NoError(t, err, "Unexpected error writing to WriteSyncer.")
		assert.Error(t, ws.Stop(), "Expected stop to fail.")
		assert.NoError(t, ws.Stop(), "Expected stop to not fail.")
	})

	t.Run("wrap twice", func(t *testing.T) {
		buf := &bytes.Buffer{}
		bufsync := &BufferedWriteSyncer{WS: AddSync(buf)}
		ws := &BufferedWriteSyncer{WS: bufsync}
		requireWriteWorks(t, ws)
		assert.Empty(t, buf.String(), "Unexpected log calling a no-op Write method.")
		require.NoError(t, ws.Sync())
		assert.Equal(t, "foo", buf.String())
		assert.NoError(t, ws.Stop())
		assert.NoError(t, bufsync.Stop())
		assert.Equal(t, "foo", buf.String(), "Unexpected log string")
	})

	t.Run("small buffer", func(t *testing.T) {
		buf := &bytes.Buffer{}
		ws := &BufferedWriteSyncer{WS: AddSync(buf), Size: 5}

		requireWriteWorks(t, ws)
		assert.Equal(t, "", buf.String(), "Unexpected log calling a no-op Write method.")
		requireWriteWorks(t, ws)
		assert.Equal(t, "foo", buf.String(), "Unexpected log string")
		assert.NoError(t, ws.Stop())
	})

	t.Run("with lockedWriteSyncer", func(t *testing.T) {
		buf := &bytes.Buffer{}
		ws := &BufferedWriteSyncer{WS: Lock(AddSync(buf)), Size: 5}

		requireWriteWorks(t, ws)
		assert.Equal(t, "", buf.String(), "Unexpected log calling a no-op Write method.")
		requireWriteWorks(t, ws)
		assert.Equal(t, "foo", buf.String(), "Unexpected log string")
		assert.NoError(t, ws.Stop())
	})

	t.Run("flush error", func(t *testing.T) {
		ws := &BufferedWriteSyncer{WS: &ztest.FailWriter{}, Size: 4}
		n, err := ws.Write([]byte("foo"))
		require.NoError(t, err, "Unexpected error writing to WriteSyncer.")
		require.Equal(t, 3, n, "Wrote an unexpected number of bytes.")
		_, err = ws.Write([]byte("foo"))
		assert.Error(t, err, "Expected error writing to WriteSyncer.")
		assert.Error(t, ws.Stop(), "Expected stop to fail.")
	})

	t.Run("flush timer", func(t *testing.T) {
		buf := &bytes.Buffer{}
		clock := ztest.NewMockClock()
		ws := &BufferedWriteSyncer{
			WS:            AddSync(buf),
			Size:          6,
			FlushInterval: time.Microsecond,
			Clock:         clock,
		}
		requireWriteWorks(t, ws)
		clock.Add(10 * time.Microsecond)
		assert.Equal(t, "foo", buf.String(), "Unexpected log string")

		// flush twice to validate loop logic
		requireWriteWorks(t, ws)
		clock.Add(10 * time.Microsecond)
		assert.Equal(t, "foofoo", buf.String(), "Unexpected log string")
		assert.NoError(t, ws.Stop())
	})
}