context: implement a spy response writer to check if anything is written

context/context.go

@@ -3,6 +3,7 @@ package context
 import (
 	"context"
 	"fmt"
+	"log"
 	"net/http"
 )
 
@@ -12,7 +13,11 @@ type Store interface {
 
 func Server(store Store) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		data, _ := store.Fetch(r.Context())
+		data, err := store.Fetch(r.Context())
+		if err != nil {
+			log.Println(err)
+			return
+		}
 		fmt.Fprint(w, data)
 	}
 }

context/context_test.go

@@ -2,6 +2,7 @@ package context
 
 import (
 	"context"
+	"errors"
 	"log"
 	"net/http"
 	"net/http/httptest"
@@ -39,6 +40,24 @@ func (s *SpyStore) Fetch(ctx context.Context) (string, error) {
 	}
 }
 
+type SpyResponseWriter struct {
+	written bool
+}
+
+func (s *SpyResponseWriter) Header() http.Header {
+	s.written = true
+	return nil
+}
+
+func (s *SpyResponseWriter) Write([]byte) (int, error) {
+	s.written = true
+	return 0, errors.New("not implemented")
+}
+
+func (s *SpyResponseWriter) WriteHeader(statusCode int) {
+	s.written = true
+}
+
 func TestServer(t *testing.T) {
 	t.Run("basic get store", func(t *testing.T) {
 		data := "hello, world"
@@ -55,21 +74,25 @@ func TestServer(t *testing.T) {
 		}
 	})
 
-	// t.Run("tells store to cancel work if request is cancelled", func(t *testing.T) {
-	// 	data := "hello, world"
-	// 	store := &SpyStore{response: data, t: t}
-	// 	srv := Server(store)
-	//
-	// 	request := httptest.NewRequest(http.MethodGet, "/", nil)
-	//
-	// 	cancellingCtx, cancel := context.WithCancel(request.Context())
-	// 	// Wait 5ms to call cancel
-	// 	time.AfterFunc(5*time.Millisecond, cancel)
-	//
-	// 	request = request.WithContext(cancellingCtx)
-	//
-	// 	response := httptest.NewRecorder()
-	//
-	// 	srv.ServeHTTP(response, request)
-	// })
+	t.Run("tells store to cancel work if request is cancelled", func(t *testing.T) {
+		data := "hello, world"
+		store := &SpyStore{response: data, t: t}
+		srv := Server(store)
+
+		request := httptest.NewRequest(http.MethodGet, "/", nil)
+
+		cancellingCtx, cancel := context.WithCancel(request.Context())
+		// Wait 5ms to call cancel
+		time.AfterFunc(5*time.Millisecond, cancel)
+
+		request = request.WithContext(cancellingCtx)
+
+		response := &SpyResponseWriter{}
+
+		srv.ServeHTTP(response, request)
+
+		if response.written {
+			t.Error("a response should not have been written")
+		}
+	})
 }