如何在 golang 框架中编写依赖外部服务的单元测试？

package service

// MyService 接口定义了外部服务行为
type MyService interface {
    GetData() (string, error)
}

// MyServiceMock 是 MyService 接口的模拟类型
type MyServiceMock struct {
    mock.Mock
}

// GetData 模拟外部服务的 GetData 方法
func (m *MyServiceMock) GetData() (string, error) {
    ret := m.Called()
    return ret.Get(0).(string), ret.Error(1)
}

package service

import (
    "testing"
    "time"
)

func TestService_GetData(t *testing.T) {
    // 创建模拟服务
    mockService := &MyServiceMock{}

    // 设置 mock 行为
    mockService.On("GetData").Return("sample data", nil).Once()

    service := NewService(mockService, time.Duration(0))
    data, err := service.GetData()

    // 断言
    if err != nil {
        t.Fatal(err)
    }
    if data != "sample data" {
        t.Fatalf("Expected 'sample data', got '%s'", data)
    }

    // 验证调用是否发生
    if !mockService.AssertCalled(t, "GetData") {
        t.Error("GetData() was not called")
    }
}

package service_test

import (
    "context"
    "fmt"
    "io"
    "net/http"
    "net/http/httptest"
    "strings"
    "testing"

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

func TestService_GetData(t *testing.T) {
    type args struct {
        ctx context.Context
        r   *http.Request
    }
    tests := []struct {
        name           string
        args           args
        mockStatusCode int
        expectedBody   string
    }{
        {
            "Success",
            args{context.Background(), new(http.Request)},
            http.StatusOK,
            "sample data",
        },
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            // 模拟服务端行为
            server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
                if r.Method != "GET" {
                    t.Errorf("Unexpected HTTP method: %s", r.Method)
                }

                w.WriteHeader(tt.mockStatusCode)
                _, _ = io.WriteString(w, tt.expectedBody)
            }))
            defer server.Close()

            // 更新请求以指向模拟服务端
            baseClient := Service.GetClient()
            t.Cleanup(func() { Service.SetClient(baseClient) })
            Service.SetClient(http.Client{Transport: &http.Transport{
                Base:    &http.Transport{DisableCompression: true},
                DialTLS: func(network, addr string) (net.Conn, error) {
                    return net.Dial(network, strings.Replace(addr, "localhost", server.Listener.Addr().String(), 1))
                },
            }})

            // 执行测试
            result, err := Service.GetData(tt.args.ctx, tt.args.r)
            assert.Nil(t, err)
            assert.Equal(t, tt.expectedBody, result)
        })
    }
}