我在尝试测试这个函数时遇到了麻烦，里面有一个错误。下面是我的ResponseJson函数，它不返回错误，但发送一个响应json。

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
    }
    
}

下面是我的单元测试代码，它创建了一个模拟的ResponseWriter，并且能够成功地测试编写器响应json的情况，没有错误。由于我没有在ResponseJson（）函数中返回错误类型，我如何在Test_ResponseJson函数中测试它，如下所示？

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)
        }
    }
}

此外，我还创建了一个函数，为log.Println（）内置函数生成实际的日志输出。我知道log.Println（）函数是一个内置函数，它不太可能失败。但是，我希望在我的单元测试中实现100%的覆盖率。请帮助！谢谢：）

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
}