Bagaimana untuk menggunakan suntikan pergantungan untuk ujian unit di Golang?

import (
    "context"
    "testing"

    "github.com/google/go-cmp/cmp"
)

// Interface we want to test.
type Greeter interface {
    Greet(ctx context.Context, name string) (string, error)
}

// Implementation we want to test.
type DefaultGreeter struct{}

func (g DefaultGreeter) Greet(ctx context.Context, name string) (string, error) {
    return "Hello, " + name, nil
}

func TestGreeter_Greet(t *testing.T) {
    type Fields struct {
        greeter Greeter
    }

    wire.Build(Fields{
        greeter: (*DefaultGreeter)(nil),
    })

    cases := []struct {
        setup    func(t *testing.T, fields Fields)
        expected *string
        wantErr  bool
    }{
        {
            expected: String("Hello, Bob"),
        },
    }

    for _, tc := range cases {
        tc := tc // capture range variable
        t.Run(testName, func(t *testing.T) {
            t.Parallel()

            fields := Fields{}
            tc.setup(t, fields)

            result, err := fields.greeter.Greet(context.Background(), "Bob")

            if (err != nil) != tc.wantErr {
                t.Fatalf("error = %v, wantErr = %v", err, tc.wantErr)
            }
            if tc.wantErr {
                return
            }
            if diff := cmp.Diff(*tc.expected, result); diff != "" {
                t.Fatalf("result mismatch (-want +got):\n%s", diff)
            }
        })
    }
}

import (
    "net/http"
    "net/http/httptest"
    "testing"

    "github.com/gorilla/mux"
    "github.com/stretchr/testify/assert"

    "mypkg/handlers"
)

// Interface we want to test.
type UserService interface {
    GetUser(id int) (*User, error)
}

// Implementation we want to test.
type DefaultUserService struct{}

func (s DefaultUserService) GetUser(id int) (*User, error) {
    return &User{ID: id, Name: "Bob"}, nil
}

type Request struct {
    UserService UserService
}

func (r Request) ServeHTTP(w http.ResponseWriter, req *http.Request) {
    id, err := strconv.Atoi(mux.Vars(req)["id"])
    if err != nil {
        http.Error(w, err.Error(), http.StatusBadRequest)
        return
    }
    user, err := r.UserService.GetUser(id)
    if err != nil {
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    fmt.Fprintf(w, "%s", user.Name)
}

func TestHandler_GetUser(t *testing.T) {
    r := &Request{}

    type Fields struct {
        userService UserService
    }

    wire.Build(Fields{
        userService: (*DefaultUserService)(nil),
    })

    cases := []struct {
        name string
        id   int
        body string
        want string
    }{
        {
            body: `{"body":""}`,
            want: `Bob`,
        },
        {
            id:   2,
            body: `{"body":""}`,
            want: `Bob`,
        },
    }

    for _, tc := range cases {
        tc := tc // capture range variable
        t.Run(tc.name, func(t *testing.T) {
            req, _ := http.NewRequest("GET", "/", bytes.NewBuffer([]byte(tc.body)))
            if tc.id != 0 {
                req = mux.SetURLVars(req, map[string]string{"id": strconv.Itoa(tc.id)})
            }
            rr := httptest.NewRecorder()
            handler := http.HandlerFunc(r.ServeHTTP)
            handler.ServeHTTP(rr, req)

            assert.Equal(t, tc.want, rr.Body.String())
        })
    }
}