How to correctly mock some *sql.DB methods for unit testing using interfaces? For example, I want to have a Store struct that is used as a datasource for my handlers. It has a conn field that is the *sql.DB. But in my tests I want to mock the DB, so I try to return not the actual *sql.Rows but an interface that the *sql.Rows should satisfy. Here is the code:
type TestRows interface {
Scan ()
}
type TestDB interface {
Query (query string, args ...interface{}) (TestRows, error)
}
type Rows struct {
//..
}
func (r *Rows) Scan () {
fmt.Println("Scanning")
}
This is the *sql.DB
type DB struct {
//...
}
func (d *DB) Query (query string, args ...inteface{}) (*Rows, error) {
return &Rows{/* .... */}, nil
}
And when I want to instantiate the Store, it throws error
type Store struct {
conn TestDB
}
func main() {
cl := Store {conn: &DB{}}
fmt.Println("Hello, playground")
}
cannot use DB literal (type *DB) as type TestDB in field value:
*DB does not implement TestDB (wrong type for Query method)
have Query(string) (*Rows, error)
want Query(string) (TestRows, error)