diff --git a/internal/deepl/translate_test.go b/internal/deepl/translate_test.go
index d7efe01..b94826b 100644
--- a/internal/deepl/translate_test.go
+++ b/internal/deepl/translate_test.go
@@ -6,71 +6,79 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"net/url"
-	"path/filepath"
-	"strconv"
-	"strings"
 	"testing"
-
-	"github.com/candy12t/deepl-cli/test"
 )
 
+const defaultBaseURL = "https://api.deepl.com/v2"
+
 func TestTranslate(t *testing.T) {
-	t.Run("success translate", func(t *testing.T) {
-		client, server, err := deeplMockServer(t, "test-auth-key", "success-body", "success-header")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer server.Close()
+	client, mux, teardown := setup()
+	defer teardown()
+	body := `{"translations":[{"detected_source_language":"EN","text":"こんにちわ"}]}`
+	want := "こんにちわ"
 
-		ctx := context.Background()
-		got, err := client.Translate(ctx, "hello", "EN", "JA")
-		if err != nil {
-			t.Fatal(err)
-		}
-		want := "こんにちわ"
+	mux.HandleFunc(TRANSLATE, func(w http.ResponseWriter, r *http.Request) {
+		testHeader(t, r, "Content-Type", "application/x-www-form-urlencoded")
+		testHeader(t, r, "Authorization", "DeepL-Auth-Key test-auth-key")
+		testMethod(t, r, "POST")
+		testBody(t, r, "source_lang=EN&target_lang=JA&text=hello")
 
-		if got != want {
-			t.Fatalf("got %v, want %v", got, want)
-		}
+		w.WriteHeader(http.StatusOK)
+		w.Write([]byte(body))
 	})
+
+	ctx := context.Background()
+	got, err := client.Translate(ctx, "hello", "EN", "JA")
+	assertNoErr(t, err)
+	assertTranslatedText(t, got, want)
 }
 
-func deeplMockServer(t *testing.T, mockAuthKey string, mockResponseBody, mockResponseHeader string) (*Client, *httptest.Server, error) {
-	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		header := filepath.Join(test.ProjectDirPath(), "test", "testdata", "deepl", mockResponseHeader)
-		headerBytes, err := ioutil.ReadFile(header)
-		h := strings.Split(string(headerBytes), "\n")
-		for _, line := range h {
-			if strings.Contains(line, "HTTP") {
-				statusCode, err := strconv.Atoi(strings.Split(line, " ")[1])
-				if err != nil {
-					t.Fatal(err)
-				}
-				w.WriteHeader(statusCode)
-			}
+func setup() (*Client, *http.ServeMux, func()) {
+	mux := http.NewServeMux()
+	server := httptest.NewServer(mux)
 
-			if strings.Contains(line, "content-type") {
-				contentType := strings.Split(line, " ")[1]
-				w.Header().Add("content-type", contentType)
-			}
-		}
+	client, _ := NewClient(defaultBaseURL, "test-auth-key")
+	url, _ := url.ParseRequestURI(server.URL)
+	client.BaseURL = url
 
-		body := filepath.Join(test.ProjectDirPath(), "test", "testdata", "deepl", mockResponseBody)
-		bodyBytes, err := ioutil.ReadFile(body)
-		if err != nil {
-			t.Fatal(err)
-		}
-		w.Write(bodyBytes)
-	}))
+	return client, mux, server.Close
+}
 
-	serverURL, err := url.ParseRequestURI(server.URL)
+func testBody(t *testing.T, r *http.Request, want string) {
+	t.Helper()
+	b, err := ioutil.ReadAll(r.Body)
 	if err != nil {
-		return nil, nil, err
+		t.Errorf("Error reading request body: %v", err)
+	}
+	if got := string(b); got != want {
+		t.Errorf("request Body is %s, want %s", got, want)
+	}
+}
+
+func testMethod(t *testing.T, r *http.Request, want string) {
+	t.Helper()
+	if got := r.Method; got != want {
+		t.Errorf("Request method: %v, want %v", got, want)
 	}
+}
+
+func testHeader(t *testing.T, r *http.Request, header string, want string) {
+	t.Helper()
+	if got := r.Header.Get(header); got != want {
+		t.Errorf("Header.Get(%q) returned %q, want %q", header, got, want)
+	}
+}
 
-	return &Client{
-		BaseURL:    serverURL,
-		HTTPClient: server.Client(),
-		AuthKey:    mockAuthKey,
-	}, server, nil
+func assertTranslatedText(t *testing.T, got, want string) {
+	t.Helper()
+	if got != want {
+		t.Errorf("translated text is %s, want %s", got, want)
+	}
+}
+
+func assertNoErr(t *testing.T, got error) {
+	t.Helper()
+	if got != nil {
+		t.Fatal("got an error but didn't want one")
+	}
 }