I am trying to wrap my head around dependency injection in Go, but really stuck here. Here's a (drastically simplified) app which should serve as an example:
package main
import (
"net/http"
"github.com/gorilla/mux"
)
func main() {
mux := mux.NewRouter()
mux.Handle("/", myHandler()).Methods("GET")
http.ListenAndServe(":9000", mux)
}
type myObject interface {
Start()
}
type Object struct {
}
func (o *Object) Start() {
// Something wild here, for example sending out an email,
// query an external DB or something similar..
}
func myHandler() http.Handler {
// Inject myObject-like struct somewhere here?
o := Object{}
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
o.Start()
w.Write([]byte("Started Object"))
})
}
I have a problem with testing the Object struct. What I usually do is create an interface which can be used in testing by setting up a test struct. For instance, if I had a DB connection handler, in testing I can create a mock which satisfies the handler interface and pass this to the "myHandler" call as a parmeter.
Unfortunately this only works if the struct is already instantiated when the "mux.Handle" call is made. I simply don't see any simple way to test the myHandler function with an Object struct which can be injected in tests, since it will be created after the handler gets called.
Any hints or ideas on how to get this done? Maybe I have to rethink my testing approach, but I would really like to unit-test the Object struct, but also test the http handler separately (as this handler may perform more tasks than just creating the Object).
