How to simulate db ping without sqlmock

When developing software, we often encounter situations where we need to simulate database connections for testing. However, sometimes we may not have a tool like sqlmock to help us achieve this goal. So, how should we simulate the ping operation of the database without sqlmock? In this article, PHP editor Youzi will introduce you to a simple and effective method to achieve this goal, allowing you to successfully conduct simulation tests of database connections.

Question content

I would like to understand how to use mock.mock to refactor my code to simulate db.ping(). I want to understand this concept without a framework first.

This is the code I want to test:

func Connect() (*sql.DB, error) {

    db, err := sql.Open("mysql", "root:secret@tcp(s-maria-db)/s_db")

    if err != nil {
        return nil, err
    }

    for i := 0; i < 60; i++ {
        // I am hoping to mock this portion
        if err := db.Ping(); err == nil {
            break
        }
        time.Sleep(time.Second)
    }

    return db, nil
}

I tried this article on how to simulate a ping command, but that doesn't actually answer the question. If so, I don't understand the solution as it works for my code.

Workaround

You need to use a separate function for ping, and it needs to accept an interface so that you can conditionally pass in the real *sql.db or simulation. This is because you cannot override methods on a structure.

// connect opens a connection to the database.
func connect() (*sql.db, error) {
    return sql.open("mysql", "root:secret@tcp(s-maria-db)/s_db")
}

// pinger defines an interface for pinging.
type pinger interface {
    ping() error
}

// ping attempts to ping the database, trying several times before failing.
func ping(p pinger) error {
    const maxattempts = 60
    var err error
    for i := 0; i < maxattempts; i++ {
        if err = p.ping(); err == nil {
            return nil
        }
        if i < maxattempts - 1 {
            time.sleep(time.second)
        }
    }
    return err
}

func main() {
    if err := run(); err != nil {
        log.fatal(err)
    }
}

func run() error {
    db, err := connect()
    if err != nil {
        return fmt.errorf("connecting to db: %w", err)
    }
    defer db.close()

    if err = ping(db); err != nil {
        return fmt.errorf("pinging db: %w", err)
    }
    
    ...
}

type mockDB struct {
    mock.Mock
}

func (m *mockDB) Ping() error {
    args := m.Called()
    return args.Error(0)
}

func TestPing(t *testing.T) {
    db := &mockDB{}
    db.On("Ping").Return(...)

    err := Ping(db)

    ...
    db.AssertExpectations(t)
}

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