如何在 Go 中模拟将结果写入其参数的函数

Question

我正在通过https://github.com/stretchr/testify在 golang 中编写单元测试 假设我有下面的方法，

func DoSomething(result interface{}) error {
    // write some data to result
    return nil
}

所以调用者可以调用DoSomething如下

result := &SomeStruct{}
err := DoSomething(result)

if err != nil {
  fmt.Println(err)
} else {
  fmt.Println("The result is", result)
}

现在我知道如何使用testify或其他一些模拟工具来模拟返回值（它在err这里）

mockObj.On("DoSomething", mock.Anything).Return(errors.New("mock error"))

我的问题是result在这种情况下“我如何嘲笑论点”？

由于result不是返回值而是参数，调用者通过传递一个结构体的指针来调用它，然后函数修改它。

Answer 1

您可以使用以下(*Call).Run方法：

Run 设置在返回之前要调用的处理程序。它可以在模拟一个方法（例如解组器）时使用，该方法采用指向结构的指针并在此类结构中设置属性

例子：

Mock.On("Unmarshal", AnythingOfType("*map[string]interface{}").Return().Run(func(args Arguments) {
    arg := args.Get(0).(*map[string]interface{})
    arg["foo"] = "bar"
})

Answer 2

正如@bikbah所说，这是一个例子：

services/message.go:

type messageService struct {
    HttpClient http.Client
    BaseURL    string
}
func (m *messageService) MarkAllMessages(accesstoken string) []*model.MarkedMessage {
    endpoint := m.BaseURL + "/message/mark_all"
    var res model.MarkAllMessagesResponse
    if err := m.HttpClient.Post(endpoint, &MarkAllMessagesRequestPayload{Accesstoken: accesstoken}, &res); err != nil {
        fmt.Println(err)
        return res.MarkedMsgs
    }
    return res.MarkedMsgs
}

我们传递res给该m.HttpClient.Post方法。在此方法中，res将填充json.unmarshal方法。

mocks/http.go:

package mocks

import (
    "io"

    "github.com/stretchr/testify/mock"
)

type MockedHttp struct {
    mock.Mock
}

func (m *MockedHttp) Get(url string, data interface{}) error {
    args := m.Called(url, data)
    return args.Error(0)
}

func (m *MockedHttp) Post(url string, body interface{}, data interface{}) error {
    args := m.Called(url, body, data)
    return args.Error(0)
}

services/message_test.go:

package services_test

import (
    "errors"
    "reflect"
    "strconv"
    "testing"

    "github.com/stretchr/testify/mock"
    "github.com/mrdulin/gqlgen-cnode/graph/model"
    "github.com/mrdulin/gqlgen-cnode/services"
    "github.com/mrdulin/gqlgen-cnode/mocks"
)

const (
    baseURL     string = "http://localhost/api/v1"
    accesstoken string = "123"
)

func TestMessageService_MarkAllMessages(t *testing.T) {
    t.Run("should mark all messaages", func(t *testing.T) {
        testHttp := new(mocks.MockedHttp)
        var res model.MarkAllMessagesResponse
        var markedMsgs []*model.MarkedMessage
        for i := 1; i <= 3; i++ {
            markedMsgs = append(markedMsgs, &model.MarkedMessage{ID: strconv.Itoa(i)})
        }
        postBody := services.MarkAllMessagesRequestPayload{Accesstoken: accesstoken}
        testHttp.On("Post", baseURL+"/message/mark_all", &postBody, &res).Return(nil).Run(func(args mock.Arguments) {
            arg := args.Get(2).(*model.MarkAllMessagesResponse)
            arg.MarkedMsgs = markedMsgs
        })
        service := services.NewMessageService(testHttp, baseURL)
        got := service.MarkAllMessages(accesstoken)
        want := markedMsgs
        testHttp.AssertExpectations(t)
        if !reflect.DeepEqual(got, want) {
            t.Errorf("got wrong return value. got: %#v, want: %#v", got, want)
        }
    })

    t.Run("should print error and return empty slice", func(t *testing.T) {
        var res model.MarkAllMessagesResponse
        testHttp := new(mocks.MockedHttp)
        postBody := services.MarkAllMessagesRequestPayload{Accesstoken: accesstoken}
        testHttp.On("Post", baseURL+"/message/mark_all", &postBody, &res).Return(errors.New("network"))
        service := services.NewMessageService(testHttp, baseURL)
        got := service.MarkAllMessages(accesstoken)
        var want []*model.MarkedMessage
        testHttp.AssertExpectations(t)
        if !reflect.DeepEqual(got, want) {
            t.Errorf("got wrong return value. got: %#v, want: %#v", got, want)
        }
    })
}

在单元测试用例中，我们填充了res# Call.Run方法并将返回值( res.MarkedMsgs)分配service.MarkAllMessages(accesstoken)给got变量。

单元测试结果和覆盖率：

=== RUN   TestMessageService_MarkAllMessages
--- PASS: TestMessageService_MarkAllMessages (0.00s)
=== RUN   TestMessageService_MarkAllMessages/should_mark_all_messaages
    TestMessageService_MarkAllMessages/should_mark_all_messaages: message_test.go:39: PASS: Post(string,*services.MarkAllMessagesRequestPayload,*model.MarkAllMessagesResponse)
    --- PASS: TestMessageService_MarkAllMessages/should_mark_all_messaages (0.00s)
=== RUN   TestMessageService_MarkAllMessages/should_print_error_and_return_empty_slice
network
    TestMessageService_MarkAllMessages/should_print_error_and_return_empty_slice: message_test.go:53: PASS: Post(string,*services.MarkAllMessagesRequestPayload,*model.MarkAllMessagesResponse)
    --- PASS: TestMessageService_MarkAllMessages/should_print_error_and_return_empty_slice (0.00s)
PASS
coverage: 5.6% of statements in ../../gqlgen-cnode/...

Process finished with exit code 0