Einfaches Fehlerproblem beim Golang-Unit-Testen

func responsejson(w http.responsewriter, code int, message string) {
    jsonstatus := struct {
        code int `json:"code"`
        message string `json:"message"`
    }{
        message: message,
        code: code,
    }

    bs, err := json.marshal(jsonstatus);

    if err != nil {
        log.println("error in marshal json in responsejson: ", err)
        str := "internal server error. please contact the system administrator."
        io.writestring(w, str);
        return 
    } else {
        io.writestring(w, string(bs));
        return
    }
    
}

func test_responsejson(t *testing.t) {
    responsejsontests := []struct {
        testname string
        code int
        message string
        expectedjsonresponse string
    } {
        {"successful login", http.statusok, "successfully logged in!", `{"code":200,"message":"successfully logged in!"}`},
        {"existing username", http.statusbadrequest, "username already exists. please try again.", `{"code":400,"message":"username already exists. please try again."}`},
    }

    for _, e := range responsejsontests {
        // creating a mock responsewriter
        w := httptest.newrecorder()

        responsejson(w, e.code, e.message)

        // read the response body as a string
        body, _ := io.readall(w.result().body)
        actual := string(body)

        expected := e.expectedjsonresponse
        if actual != expected {
            t.errorf("%s: expected %s but got %s", e.testname, e.expectedjsonresponse, actual)
        }
    }
}

func GenerateLogOutput(message string, errorMessage string) string {
    // Create a new bytes.Buffer to capture the log output
    var buf bytes.Buffer

    // Redirect log output to a different destination set as a buffer
    // By default, log message are written to the standard error stream os.Stderr
    log.SetOutput(&buf)

    // Generate an error
    err := errors.New(errorMessage)

    w := httptest.NewRecorder()

    // Calling the function
    InternalServerError(w, message, err)
    actualOutput := buf.String()

    return actualOutput
}

func Test_ResponseJson(t *testing.T) {
    tests := []struct {
        Code        int
        Message     string
        ExpectedStr string
    }{
        {
            Code:        1,
            Message:     "sample message",
            ExpectedStr: "{\"code\":1,\"message\":\"sample message\"}",
        },
    }
    for _, test := range tests {
        w := httptest.NewRecorder()

        ResponseJson(w, test.Code, test.Message)

        res := w.Result()
        data, err := ioutil.ReadAll(res.Body)
        res.Body.Close()

        actualStr := string(data)

        assert.Nil(t, err, "Invalid test data")
        assert.Equal(t, actualStr, test.ExpectedStr)
    }
}