diff --git a/kadai4/en-ken/kadai4/export_test.go b/kadai4/en-ken/kadai4/export_test.go
new file mode 100644
index 0000000..f3e1aff
--- /dev/null
+++ b/kadai4/en-ken/kadai4/export_test.go
@@ -0,0 +1,20 @@
+package main
+
+import (
+	"time"
+)
+
+var GetFortune = getFortune
+var Handler = handler
+
+func SetNow(n func() time.Time) {
+	now = n
+}
+
+func SetFortunes(f []string) {
+	fortunes = f
+}
+
+func SetNewEncoder(n NewEncoder) {
+	newEncoder = n
+}
diff --git a/kadai4/en-ken/kadai4/fortune.go b/kadai4/en-ken/kadai4/fortune.go
new file mode 100644
index 0000000..7eebd47
--- /dev/null
+++ b/kadai4/en-ken/kadai4/fortune.go
@@ -0,0 +1,29 @@
+package main
+
+import (
+	"math/rand"
+	"time"
+)
+
+// For testing
+var now = time.Now
+var fortunes []string
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+	fortunes = []string{"大吉", "吉", "中吉", "小吉", "末吉", "凶", "大凶"}
+}
+
+func getFortune() string {
+	i := rand.Int() % len(fortunes)
+	f := fortunes[i]
+
+	t := now()
+	if t.Month() == 1 {
+		if t.Day() >= 1 && t.Day() <= 3 {
+			f = "大吉"
+		}
+	}
+
+	return f
+}
diff --git a/kadai4/en-ken/kadai4/fortune_test.go b/kadai4/en-ken/kadai4/fortune_test.go
new file mode 100644
index 0000000..56b80f1
--- /dev/null
+++ b/kadai4/en-ken/kadai4/fortune_test.go
@@ -0,0 +1,64 @@
+package main_test
+
+import (
+	"fmt"
+	"testing"
+	"time"
+
+	main "github.com/gopherdojo/dojo6/kadai4/en-ken/kadai4"
+)
+
+func TestGetLuck(t *testing.T) {
+
+	cases := []struct {
+		now      time.Time
+		expected string
+	}{
+		{
+			now:      time.Date(2018, time.December, 31, 0, 0, 0, 0, time.Local),
+			expected: "凶",
+		},
+		{
+			now:      time.Date(2018, time.December, 31, 23, 59, 59, 999, time.Local),
+			expected: "凶",
+		},
+		{
+			now:      time.Date(2019, time.January, 1, 0, 0, 0, 0, time.Local),
+			expected: "大吉",
+		},
+		{
+			now:      time.Date(2019, time.January, 2, 0, 0, 0, 0, time.Local),
+			expected: "大吉",
+		},
+		{
+			now:      time.Date(2019, time.January, 3, 0, 0, 0, 0, time.Local),
+			expected: "大吉",
+		},
+		{
+			now:      time.Date(2018, time.January, 3, 23, 59, 59, 999, time.Local),
+			expected: "大吉",
+		},
+		{
+			now:      time.Date(2019, time.January, 4, 0, 0, 0, 0, time.Local),
+			expected: "凶",
+		},
+	}
+
+	main.SetFortunes([]string{"凶", "凶", "凶"})
+
+	for i, c := range cases {
+		c := c
+		t.Run(
+			fmt.Sprintf("case[%v]", i),
+			func(t *testing.T) {
+				main.SetNow(func() time.Time {
+					return c.now
+				})
+
+				if actual := main.GetFortune(); actual != c.expected {
+					t.Errorf("actual:%v, expected:%v\n", actual, c.expected)
+				}
+			})
+	}
+
+}
diff --git a/kadai4/en-ken/kadai4/main.go b/kadai4/en-ken/kadai4/main.go
new file mode 100644
index 0000000..dd31146
--- /dev/null
+++ b/kadai4/en-ken/kadai4/main.go
@@ -0,0 +1,45 @@
+package main
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+)
+
+// Encoder is I/F to json.Encoder
+type Encoder interface {
+	Encode(v interface{}) error
+}
+
+// NewEncoder is I/F to json.NewEncoder
+type NewEncoder func(w io.Writer) Encoder
+
+var newEncoder NewEncoder
+
+func init() {
+	// For testing
+	newEncoder = func(w io.Writer) Encoder {
+		return json.NewEncoder(w)
+	}
+}
+
+func main() {
+	http.HandleFunc("/", handler)
+	http.ListenAndServe(":8080", nil)
+}
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set("Content-Type", "applicaiton/json; charset=utf-8")
+
+	enc := newEncoder(w)
+
+	resp := &struct {
+		Fortune string `json:"fortune"`
+	}{
+		Fortune: getFortune(),
+	}
+
+	if err := enc.Encode(resp); err != nil {
+		http.Error(w, "Server error", http.StatusInternalServerError)
+	}
+}
diff --git a/kadai4/en-ken/kadai4/main_test.go b/kadai4/en-ken/kadai4/main_test.go
new file mode 100644
index 0000000..1b970bb
--- /dev/null
+++ b/kadai4/en-ken/kadai4/main_test.go
@@ -0,0 +1,79 @@
+package main_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	main "github.com/gopherdojo/dojo6/kadai4/en-ken/kadai4"
+)
+
+type data struct {
+	Fortune string `json:"fortune"`
+}
+
+func TestServer(t *testing.T) {
+	ts := httptest.NewServer(http.HandlerFunc(main.Handler))
+	defer ts.Close()
+
+	res, err := http.Get(ts.URL)
+	if err != nil {
+		t.Errorf("Response error:%v", err)
+	}
+
+	var d data
+	if err = json.NewDecoder(res.Body).Decode(&d); err != nil {
+		t.Errorf("Data format error:%v", err)
+	}
+}
+
+type EncoderMock struct {
+}
+
+func NewEncoderMock(w io.Writer) main.Encoder {
+	return &EncoderMock{}
+}
+
+func (enc *EncoderMock) Encode(v interface{}) error {
+	return fmt.Errorf("Internal server error")
+}
+
+func TestServerInternalServerError(t *testing.T) {
+	main.SetNewEncoder(NewEncoderMock)
+	defer main.SetNewEncoder(main.NewEncoder(func(w io.Writer) main.Encoder {
+		return json.NewEncoder(w)
+	}))
+
+	ts := httptest.NewServer(http.HandlerFunc(main.Handler))
+	defer ts.Close()
+
+	res, _ := http.Get(ts.URL)
+	if res.StatusCode != 500 {
+		t.Errorf("Response code error:%v", res.StatusCode)
+	}
+
+}
+
+func TestHandler(t *testing.T) {
+	r := httptest.NewRequest("GET", "/", nil)
+	w := httptest.NewRecorder()
+	main.SetFortunes([]string{"大凶"})
+
+	main.Handler(w, r)
+
+	if w.Code != 200 {
+		t.Errorf("Invalid code: %v", w.Code)
+	}
+	if w.Header().Get("Content-Type") != "applicaiton/json; charset=utf-8" {
+		t.Errorf("Insufficient headers: %v", w.Header())
+	}
+	body := w.Body
+	dec := json.NewDecoder(body)
+	var d data
+	if err := dec.Decode(&d); err != nil || d.Fortune != "大凶" {
+		t.Errorf("Failed to decode: %v", err)
+	}
+}
diff --git a/kadai4/en-ken/reame.md b/kadai4/en-ken/reame.md
new file mode 100644
index 0000000..6cd0128
--- /dev/null
+++ b/kadai4/en-ken/reame.md
@@ -0,0 +1,14 @@
+# 課題4
+
+おみくじ API を作りましょう
+
+- JSON形式でおみくじの結果を返す
+- 正月 (1/1-1/3) だけ大吉にする
+- ハンドラのテストを書いてみる
+
+## 使い方
+
+```go
+go get github.com/gopherdojo/dojo6/kadai4/en-ken/kadai4
+kadai4
+```