diff --git a/.github/workflows/release.yml b/.github/workflows/release.yml
index 664212e..3e1bf49 100644
--- a/.github/workflows/release.yml
+++ b/.github/workflows/release.yml
@@ -14,11 +14,11 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v3
       - name: Set up Go
-        uses: actions/setup-go@v3
+        uses: actions/setup-go@v4
         with:
-          go-version: 1.19
+          go-version: "1.20"
       - name: Run GoReleaser
-        uses: goreleaser/goreleaser-action@v3
+        uses: goreleaser/goreleaser-action@v4
         with:
           version: latest
           args: release --rm-dist
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 5a2d5c6..7991c5d 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -5,13 +5,13 @@ jobs:
     strategy:
       matrix:
         go:
-          - 1.18.5
-          - 1.19
+          - "1.19"
+          - "1.20"
     name: Build
     runs-on: ubuntu-latest
     steps:
       - name: Set up Go
-        uses: actions/setup-go@v3
+        uses: actions/setup-go@v4
         with:
           go-version: ${{ matrix.go }}
         id: go
diff --git a/tracer.go b/tracer.go
index abff49e..6d5fca0 100644
--- a/tracer.go
+++ b/tracer.go
@@ -35,6 +35,7 @@ type Tracer struct {
 	sns      *sns.Client
 	timeline *Timeline
 	buf      *bytes.Buffer
+	w        io.Writer
 
 	now       time.Time
 	headBegin time.Time
@@ -113,6 +114,7 @@ func NewWithConfig(config aws.Config) (*Tracer, error) {
 			seen: make(map[string]bool),
 		},
 		buf: new(bytes.Buffer),
+		w:   os.Stdout,
 	}, nil
 }
 
@@ -130,6 +132,10 @@ type RunOption struct {
 	Duration    time.Duration
 }
 
+func (t *Tracer) SetOutput(w io.Writer) {
+	t.w = w
+}
+
 func (t *Tracer) Run(ctx context.Context, cluster string, taskID string, opt *RunOption) error {
 	t.now = time.Now()
 	t.option = opt
@@ -158,8 +164,8 @@ func (t *Tracer) Run(ctx context.Context, cluster string, taskID string, opt *Ru
 func (t *Tracer) report(ctx context.Context, cluster, taskID string) {
 	opt := t.option
 	if opt.Stdout {
-		fmt.Fprintln(os.Stdout, subject(cluster, taskID))
-		if _, err := t.WriteTo(os.Stdout); err != nil {
+		fmt.Fprintln(t.w, subject(cluster, taskID))
+		if _, err := t.WriteTo(t.w); err != nil {
 			fmt.Fprintln(os.Stderr, err)
 		}
 	}