Unit Testing Postgres db connection golang - postgresql

Question

I am expected to have 80% test coverage even for pushing the basic project structure. I am a bit confused how do I write unit tests for the following code to Connect to postgres db and ping postgres for health check. Can someone help me please.
var postgres *sql.DB
// ConnectToPostgres func to connect to postgres
func ConnectToPostgres(connStr string) (*sql.DB, error) {
db, err := sql.Open("postgres", connStr)
if err != nil {
log.Println("postgres-client ", err)
return nil, err
}
postgres = db
return db, nil
}
// PostgresHealthCheck to ping database and check for errors
func PostgresHealthCheck() error {
if err := postgres.Ping(); err != nil {
return err
}
return nil
}
type PostgresRepo struct {
db *sql.DB
}
// NewPostgresRepo constructor
func NewPostgresRepo(database *sql.DB) *PostgresRepo {
return &PostgresRepo{
db: database,
}
}

Answer 1

You need to use this : https://github.com/DATA-DOG/go-sqlmock
Its very easy to use. Here is an example where a controller is getting tested using a mocked SQL :
Implementation
func (up UserProvider) GetUsers() ([]models.User, error) {
var users = make([]models.User, 0, 10)
rows, err := up.DatabaseProvider.Query("SELECT firstname, lastname, email, age FROM Users;")
if err != nil {
return nil, err
}
for rows.Next() {
var u models.User = models.User{}
err := rows.Scan(&u.Name, &u.Lastname, &u.Email, &u.Age)
if err != nil {
return nil, err
}
users = append(users, u)
}
if err := rows.Err(); err != nil {
return nil, err
}
return users, nil
}
Test
func TestGetUsersOk(t *testing.T) {
db, mock := NewMock()
mock.ExpectQuery("SELECT firstname, lastname, email, age FROM Users;").
WillReturnRows(sqlmock.NewRows([]string{"firstname", "lastname", "email", "age"}).
AddRow("pepe", "guerra", "pepe#gmail.com", 34))
subject := UserProvider{
DatabaseProvider: repositories.NewMockDBProvider(db, nil),
}
resp, err := subject.GetUsers()
assert.Nil(t, err)
assert.NotNil(t, resp)
assert.Equal(t, 1, len(resp))
}
func NewMock() (*sql.DB, sqlmock.Sqlmock) {
db, mock, err := sqlmock.New()
if err != nil {
log.Fatalf("an error '%s' was not expected when opening a stub database connection", err)
}
return db, mock
}

Answer 2

I find that writing tests against a live database makes for more high quality tests. The challenge with Postgres is that there's no good in-memory fake that you can substitute in.
What I came up with is standing up the postgres Docker container and creating temporary databases in there. The PostgresContainer type in the github.com/bitcomplete/sqltestutil package does exactly this:
# Postgres version is "12"
pg, _ := sqltestutil.StartPostgresContainer(context.Background(), "12")
defer pg.Shutdown(ctx)
db, err := sql.Open("postgres", pg.ConnectionString())
// ... execute SQL
Per the docs, it's a good idea to set up your tests so that the container is only started once, as it can take a few seconds to start up (more if the image needs to be downloaded). It suggests some approaches for mitigating that problem.