FizzBuzz web server test

main.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"strconv"
)

func main() {
	log.SetFlags(log.Lshortfile | log.LstdFlags)

	http.HandleFunc("/fizzbuzz", fizzbuzz)

	log.Print("Server listening.  Press CTRL+C to terminate.")
	http.ListenAndServe(":1234", nil)
}

func fizzbuzz(w http.ResponseWriter, r *http.Request) {
	raw := r.Header.Get("n")
	if raw == "" {
		http.Error(w, "missing n request header", http.StatusBadRequest)
		return
	}

	n, err := strconv.Atoi(raw)
	if err != nil {
		http.Error(w, fmt.Sprintf("%q is not a valid number", raw), http.StatusBadRequest)
		return
	}

	if n == 0 {
		return
	}

	for i := 1; i <= n; i++ {
		w.Write([]byte(fmt.Sprintf("%s\n", toFizzBuzz(i))))
	}
}

func toFizzBuzz(i int) (out string) {
	switch {
	case i%15 == 0:
		return "buzzfizz"
	case i%3 == 0:
		return "buzz"
	case i%5 == 0:
		return "fizz"
	default:
		return strconv.Itoa(i)
	}
}

main_test.go

package main

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

func TestToFizzBuzz(t *testing.T) {
	cases := []struct {
		name string
		i    int
		exp  string
	}{
		{
			name: "3",
			i:    3,
			exp:  "buzz",
		},
		{
			name: "5",
			i:    5,
			exp:  "fizz",
		},
		{
			name: "15",
			i:    15,
			exp:  "buzzfizz",
		},
	}

	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			act := toFizzBuzz(c.i)
			if act != c.exp {
				t.Fatalf("exp %q but got %q", c.exp, act)
			}
		})
	}
}

func TestFizzBuzz(t *testing.T) {
	cases := []struct {
		name    string
		n       string
		expBody string
		expCode int
	}{
		{
			name:    "missing request header",
			expBody: "missing n request header\n",
			expCode: http.StatusBadRequest,
		},
		{
			name:    "non-numeric header",
			n:       "a",
			expBody: "\"a\" is not a valid number\n",
			expCode: http.StatusBadRequest,
		},
		{
			name:    "0",
			n:       "0",
			expCode: http.StatusOK,
		},
		{
			name:    "1",
			n:       "1",
			expBody: "1\n",
			expCode: http.StatusOK,
		},
		{
			name:    "10",
			n:       "10",
			expBody: "1\n2\nbuzz\n4\nfizz\nbuzz\n7\n8\nbuzz\nfizz\n",
			expCode: http.StatusOK,
		},
	}

	for _, c := range cases {
		t.Run(c.name, func(t *testing.T) {
			req := httptest.NewRequest(http.MethodGet, "/anything", nil)
			if c.n != "" {
				req.Header.Set("n", c.n)
			}

			resp := httptest.NewRecorder()

			fizzbuzz(resp, req)

			if resp.Code != c.expCode {
				t.Fatalf("exp %d but got %d", http.StatusOK, resp.Code)
			}
			if resp.Body.String() != c.expBody {
				t.Fatalf("exp %q but got %q", c.expBody, resp.Body.String())
			}
		})
	}
}