使用 Golang 依赖注入模拟数据库的单元测试

我正在使用 golang 接口创建一个模拟数据库来测试我的处理程序函数。但是，我似乎没有在单元测试环境中正确执行依赖项注入。我创建了一个 setup_test.go 文件来设置我的模拟数据库环境。在下面的代码片段中，我将介绍依赖注入的工作流程。

1. main.go

package main

type application struct {
    db repository.databaserepo
}

func main() {
    app := application{}

    conn, err := app.connecttodb()
    if err != nil {
        log.fatal("failed to connect to postgresql:", err)
    }

    defer func() {
        conn.close(context.background())
    }()

    app.db = &dbrepo.postgresdbrepo{db: conn}

    // passing app.db to routes function for di
    mux := routes.routes(app.db)

package repository

type databaserepo interface {
    connection() *pgx.conn
    getcountbyusername(ctx context.context, username string) (int, error)
}

package routes

func routes(app repository.databaserepo) http.handler {
    mux := chi.newrouter()

    signuph := user.new(app)
    mux.post("/signup", utils.makehttphandler(signuph.signup))
}

package user

type application struct {
    db repository.databaserepo
}

// dependency injection of repository (database)
func new(app repository.databaserepo) *application {
    return &application{db: app}
}

func (app application) signup(w http.responsewriter, req *http.request) error {
    // some other logic

    // when i run `go run .`, this prints out to be *dbrepo.postgresdbrepo
    // when i run `go test -v ./...`, this prints out to be <nil> 
    // but the expected type should be *dbrepo.testdbrepo
    fmt.printf("type of app.db: %tn", app.db)

    // fails on this line in unit testing
    usercount, err := app.db.getcountbyusername(ctx, username)

    // some other logic
}

package main

var app application

func TestMain(m *testing.M) {

    app.DB = &dbrepo.TestDBRepo{}

    fmt.Printf("Type of app.DB: %Tn", app.DB) // output type is *dbrepo.TestDBRepo

    os.Exit(m.Run())
}