go handler test example

handler.go

package main

import (
	"fmt"
	"net/http"
)

type Repo interface {
	GetOne() string
}

type PostRepo struct{}

func (pr *PostRepo) GetOne() string {
	return "some random stuff"
}

func homepageHandler(repo Repo) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		fmt.Fprintf(w, repo.GetOne())
	}
}

func postHandler() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if r.Method != http.MethodPost {
			return
		}

		r.ParseForm()

		fmt.Fprintf(w, r.FormValue("username"))
	}
}

func main() {
	repo := &PostRepo{}
	http.HandleFunc("/", homepageHandler(repo))
	http.HandleFunc("/post", postHandler())
	http.ListenAndServe(":8080", nil)
}

handler_test.go

package main

import (
	"net/http"
	"net/http/httptest"
	"net/url"
	"strings"
	"testing"
)

type testPostRepo struct{}

func (tpr *testPostRepo) GetOne() string {
	return "test"
}

type RequestFunc func(url string, params url.Values) *httptest.ResponseRecorder

func request(t *testing.T, method string, handler http.HandlerFunc) RequestFunc {
	return func(url string, params url.Values) *httptest.ResponseRecorder {
		r, err := http.NewRequest(method, url, strings.NewReader(params.Encode()))
		if err != nil {
			t.Error(err)
		}

		// only encode body when post method is used
		if method == http.MethodPost {
			r.Header.Set("Content-Type",
				"application/x-www-form-urlencoded; param=value",
			)
		}

		w := httptest.NewRecorder()

		handler(w, r)

		return w
	}
}

func TestHomepageHandler(t *testing.T) {
	repo := &testPostRepo{}

	Get := request(t, http.MethodGet, homepageHandler(repo))
	w := Get("/", url.Values{})

	got := w.Body.String()
	want := "test"

	if got != want {
		t.Fatalf("Want: %v, Got: %v\n", want, got)
	}
}

func TestPostHandler(t *testing.T) {
	Post := request(t, http.MethodPost, postHandler())
	params := url.Values{"username": []string{"John"}}
	w := Post("/post", params)

	got := w.Body.String()
	want := params.Get("username")

	if got != want {
		t.Fatalf("Want: %v, Got: %v\n", want, got)
	}
}