diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index bd6f7d7..263fc8a 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -4,7 +4,7 @@ jobs:
   test:
     strategy:
       matrix:
-        platform: [ubuntu-latest, macos-latest, windows-latest]
+        platform: [ubuntu-latest]
     runs-on: ${{ matrix.platform }}
     steps:
     - name: Install Go
@@ -14,17 +14,8 @@ jobs:
         go-version: '^1.15' # The Go version to download (if necessary) and use.
     - name: Checkout code
       uses: actions/checkout@v2
-    - name: Use Cache(on Windows)
-      if: runner.os == 'Windows'
-      uses: actions/cache@preview
-      with:
-        path: ~/go/pkg/mod
-        key: ${{ runner.os }}-go-${{ hashFiles('**\go.sum') }}
-        restore-keys: |
-          ${{ runner.os }}-go-
     - name: Use Cache
-      if: runner.os != 'Windows'
-      uses: actions/cache@preview
+      uses: actions/cache@v2
       with:
         path: ~/go/pkg/mod
         key: ${{ runner.os }}-go-${{ hashFiles('**/go.sum') }}
diff --git a/cmd/leetgode/main.go b/cmd/leetgode/main.go
index 3d5a53c..1b320ee 100644
--- a/cmd/leetgode/main.go
+++ b/cmd/leetgode/main.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"flag"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"log"
 	"os"
@@ -12,32 +13,51 @@ import (
 )
 
 func main() {
-	flag.Usage = func() {
-		if err := leetgode.ShowUsage(os.Stdout); err != nil {
-			panic(err)
+	if err := run(os.Stdout, os.Stderr, os.Args); err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	}
+}
+
+func run(stdout, stderr io.Writer, args []string) error {
+	if len(args) < 2 {
+		cmd := &leetgode.HelpCmd{}
+		if err := cmd.Run(context.Background(), stdout, []string{}); err != nil {
+			return fmt.Errorf("help command is failed: %w", err)
 		}
+		return nil
 	}
-	flag.Parse()
-	sub := flag.Arg(0)
-	if len(sub) == 0 {
-		fmt.Printf("TODO: show help\n")
-		return
+	sub := args[1]
+	// implement into each sub command if use different options by each sub command
+	f := flag.NewFlagSet(sub, flag.ContinueOnError)
+	f.Usage = func() {
+		if err := leetgode.ShowUsage(stdout); err != nil {
+			fmt.Fprintf(stderr, "failed show useage: %v\n", err)
+		}
+	}
+	var v bool
+	f.BoolVar(&v, "v", false, "show debug print")
+	if err := f.Parse(args[2:]); err == flag.ErrHelp {
+		return err
+	} else if err != nil {
+		return fmt.Errorf("%q command with invalid args(%q): %w", sub, args[2:], err)
+	}
+
+	log.SetOutput(stderr)
+	if !v {
+		log.SetOutput(ioutil.Discard)
 	}
-	// TODO: set os.Stderr if set debug mode
-	log.SetOutput(ioutil.Discard)
 
 	if cmd, ok := leetgode.CmdMap[leetgode.CmdName(sub)]; ok {
-		args := flag.Args()[1:]
+		args := f.Args()
 		if len(args) != cmd.MaxArg() {
-			fmt.Printf("%s expects %d options, but %d options\n", cmd.Name(), cmd.MaxArg(), len(args))
-			os.Exit(1)
+			return fmt.Errorf("%q command expects %d options, but %d options\n", cmd.Name(), cmd.MaxArg(), len(args))
 		}
-		if err := cmd.Run(context.Background(), args); err != nil {
-			log.Printf("main: err %v", err)
-			os.Exit(1)
+		if err := cmd.Run(context.Background(), stdout, args); err != nil {
+			return fmt.Errorf("%q command failed: %w", sub, err)
 		}
 	} else {
-		log.Printf("unknown command %q", sub)
-		os.Exit(1)
+		return fmt.Errorf("unknown command %q", sub)
 	}
+	return nil
 }
diff --git a/core.go b/core.go
index eae60d8..ee69b32 100644
--- a/core.go
+++ b/core.go
@@ -3,6 +3,7 @@ package leetgode
 import (
 	"context"
 	"fmt"
+	"io"
 )
 
 type CmdName string
@@ -20,7 +21,7 @@ type Cmd interface {
 	Name() string
 	Usage() string
 	MaxArg() int
-	Run(context.Context, []string) error
+	Run(context.Context, io.Writer, []string) error
 }
 
 var CmdMap = map[CmdName]Cmd{
diff --git a/exec.go b/exec.go
index 2cd2578..0c10a7e 100644
--- a/exec.go
+++ b/exec.go
@@ -3,6 +3,7 @@ package leetgode
 import (
 	"context"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"strconv"
@@ -26,7 +27,7 @@ func (c *ExecCmd) Usage() string {
 }
 
 // TODO: refactoring exec and test.
-func (c *ExecCmd) Run(ctx context.Context, args []string) error {
+func (c *ExecCmd) Run(ctx context.Context, out io.Writer, args []string) error {
 	id, err := strconv.Atoi(args[0])
 	if err != nil {
 		return err
@@ -51,7 +52,7 @@ func (c *ExecCmd) Run(ctx context.Context, args []string) error {
 	if err != nil {
 		return err
 	}
-	fmt.Print("now sending")
+	fmt.Fprint(out, "now sending")
 	for {
 		res, err := cli.Check(ctx, q, tr)
 		if err != nil {
@@ -59,14 +60,14 @@ func (c *ExecCmd) Run(ctx context.Context, args []string) error {
 		}
 		// FIXME: pretty print
 		if res.State == "SUCCESS" {
-			fmt.Printf(`
+			fmt.Fprintf(out, `
 executed id: %s
 problem title: %s
 result: %s
 `, q.QuestionID, q.Slug, res.StatusMsg)
 			break
 		} else {
-			fmt.Print(".")
+			fmt.Fprint(out, ".")
 		}
 		time.Sleep(1 * time.Second)
 	}
diff --git a/generate.go b/generate.go
index 127b6c5..43cdf4d 100644
--- a/generate.go
+++ b/generate.go
@@ -4,7 +4,9 @@ import (
 	"bytes"
 	"context"
 	"fmt"
+	"io"
 	"io/ioutil"
+	"log"
 	"strconv"
 	"text/template"
 
@@ -50,7 +52,7 @@ func (g *GenerateCmd) Usage() string {
 	return "Generate the skeleton code with the test file by id"
 }
 
-func (g *GenerateCmd) Run(ctx context.Context, args []string) error {
+func (g *GenerateCmd) Run(ctx context.Context, out io.Writer, args []string) error {
 	id, err := strconv.Atoi(args[0])
 	if err != nil {
 		return err
@@ -73,7 +75,7 @@ func (g *GenerateCmd) Run(ctx context.Context, args []string) error {
 	if c == nil {
 		return fmt.Errorf("not found the code for Go")
 	}
-	fmt.Printf("%s\n", fmt.Sprint(c.DefaultCode))
+	log.Printf("%s\n", fmt.Sprint(c.DefaultCode))
 	input := &Format{
 		Referer:        q.Referer,
 		Content:        q.Content,
@@ -89,11 +91,11 @@ func (g *GenerateCmd) Run(ctx context.Context, args []string) error {
 	if err != nil {
 		panic(err)
 	}
-	fmt.Printf("%s", buf.String())
+	log.Printf("%s", buf.String())
 
 	// TODO: どうやってファイル保存とテストしやすさを分けようか？
 	path := buildPath(q.QuestionID, q.Slug)
-	fmt.Printf("save at %q\n", path)
+	fmt.Fprintf(out, "save at %q\n", path)
 	if err := ioutil.WriteFile(path, buf.Bytes(), 0644); err != nil {
 		return err
 	}
diff --git a/generate_test.go b/generate_test.go
index e520040..1d4cb25 100644
--- a/generate_test.go
+++ b/generate_test.go
@@ -2,6 +2,7 @@ package leetgode
 
 import (
 	"context"
+	"io/ioutil"
 	"testing"
 )
 
@@ -17,7 +18,7 @@ func TestGenerateCmd(t *testing.T) {
 		tt := tt
 		t.Run(tt.name, func(t *testing.T) {
 			cmd := &GenerateCmd{}
-			if err := cmd.Run(context.TODO(), tt.args); err != nil {
+			if err := cmd.Run(context.TODO(), ioutil.Discard, tt.args); err != nil {
 				t.Errorf("GenerateCmd() error = %v", err)
 			}
 		})
diff --git a/help.go b/help.go
index 9d65052..08c900e 100644
--- a/help.go
+++ b/help.go
@@ -4,7 +4,6 @@ import (
 	"context"
 	"fmt"
 	"io"
-	"os"
 	"sort"
 	"text/tabwriter"
 )
@@ -49,6 +48,6 @@ func ShowUsage(w io.Writer) error {
 	return tw.Flush()
 }
 
-func (c *HelpCmd) Run(ctx context.Context, args []string) error {
-	return ShowUsage(os.Stdout)
+func (c *HelpCmd) Run(ctx context.Context, out io.Writer, args []string) error {
+	return ShowUsage(out)
 }
diff --git a/list.go b/list.go
index 846a328..f04486b 100644
--- a/list.go
+++ b/list.go
@@ -3,6 +3,7 @@ package leetgode
 import (
 	"context"
 	"fmt"
+	"io"
 	"os"
 	"sort"
 	"text/tabwriter"
@@ -24,7 +25,7 @@ func (c *ListCmd) Usage() string {
 	return "List problems"
 }
 
-func (c *ListCmd) Run(ctx context.Context, _ []string) error {
+func (c *ListCmd) Run(ctx context.Context, out io.Writer, _ []string) error {
 	cli, err := NewLeetCode()
 	if err != nil {
 		return err
diff --git a/list_test.go b/list_test.go
index 4eba5a6..37fb913 100644
--- a/list_test.go
+++ b/list_test.go
@@ -2,12 +2,13 @@ package leetgode
 
 import (
 	"context"
+	"io/ioutil"
 	"testing"
 )
 
 func TestListCmd(t *testing.T) {
 	cmd := &ListCmd{}
-	if err := cmd.Run(context.TODO(), []string{}); err != nil {
+	if err := cmd.Run(context.TODO(), ioutil.Discard, []string{}); err != nil {
 		t.Errorf("ListCmd() error = %v", err)
 	}
 }
diff --git a/pick.go b/pick.go
index c99a13e..cfed951 100644
--- a/pick.go
+++ b/pick.go
@@ -3,6 +3,7 @@ package leetgode
 import (
 	"context"
 	"fmt"
+	"io"
 	"strconv"
 )
 
@@ -23,7 +24,7 @@ func (c *PickCmd) MaxArg() int {
 	return 1
 }
 
-func (c *PickCmd) Run(ctx context.Context, args []string) error {
+func (c *PickCmd) Run(ctx context.Context, out io.Writer, args []string) error {
 	cli, err := NewLeetCode()
 	if err != nil {
 		return err
@@ -38,8 +39,8 @@ func (c *PickCmd) Run(ctx context.Context, args []string) error {
 		return err
 	}
 
-	// FIXME: pretty print
-	fmt.Printf("result: %#v\n", q)
+	// FIXME: pretty print for HTML
+	fmt.Fprintf(out, "%s: %s\n%s\n%s", q.QuestionID, q.Slug, q.Referer, q.Content)
 
 	return nil
 }
diff --git a/test.go b/test.go
index ea76a14..8bc0b78 100644
--- a/test.go
+++ b/test.go
@@ -3,6 +3,7 @@ package leetgode
 import (
 	"context"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"strconv"
@@ -25,7 +26,7 @@ func (c *TestCmd) Usage() string {
 	return "Test solution"
 }
 
-func (c *TestCmd) Run(ctx context.Context, args []string) error {
+func (c *TestCmd) Run(ctx context.Context, out io.Writer, args []string) error {
 	id, err := strconv.Atoi(args[0])
 	if err != nil {
 		return err
@@ -50,7 +51,7 @@ func (c *TestCmd) Run(ctx context.Context, args []string) error {
 	if err != nil {
 		return err
 	}
-	fmt.Print("now sending")
+	fmt.Fprint(out, "now sending")
 	for {
 		res, err := cli.Check(ctx, q, tr)
 		if err != nil {
@@ -58,14 +59,14 @@ func (c *TestCmd) Run(ctx context.Context, args []string) error {
 		}
 		// FIXME: pretty print
 		if res.State == "SUCCESS" {
-			fmt.Printf(`
+			fmt.Fprintf(out,`
 test id: %s
 problem title: %s
 result: %s
 `, q.QuestionID, q.Slug, res.StatusMsg)
 			break
 		} else {
-			fmt.Print(".")
+			fmt.Fprint(out, ".")
 		}
 		time.Sleep(1 * time.Second)
 	}