Add Unit Test for Any kind of Response on The Error Case

Author: rsdiz

19. Context/learn_context.go

@@ -29,7 +29,12 @@ type Store interface {
 
 func Server(store Store) http.HandlerFunc {
 	return func(writer http.ResponseWriter, request *http.Request) {
-		data, _ := store.Fetch(request.Context())
+		data, err := store.Fetch(request.Context())
+
+		if err != nil {
+			return // todo: log error however you like
+		}
+
 		fmt.Fprint(writer, data)
 	}
 }

19. Context/learn_context_test.go

@@ -2,15 +2,35 @@ package main
 
 import (
 	"context"
+	"errors"
 	"net/http"
 	"net/http/httptest"
 	"testing"
 	"time"
 )
 
-type SpyStore struct {
-	response string
-	t        *testing.T
+type (
+	SpyStore struct {
+		response string
+		t        *testing.T
+	}
+	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 (s *SpyStore) Fetch(ctx context.Context) (string, error) {
@@ -70,4 +90,24 @@ func TestServer(t *testing.T) {
 
 		svr.ServeHTTP(response, request)
 	})
+
+	t.Run("tells store to cancel work if request cancelled", func(t *testing.T) {
+		data := "hello, world"
+		store := &SpyStore{response: data, t: t}
+		svr := Server(store)
+
+		request := httptest.NewRequest(http.MethodGet, "/", nil)
+
+		cancellingCtx, cancel := context.WithCancel(request.Context())
+		time.AfterFunc(5*time.Millisecond, cancel)
+		request = request.WithContext(cancellingCtx)
+
+		response := &SpyResponseWriter{}
+
+		svr.ServeHTTP(response, request)
+
+		if response.written {
+			t.Error("a response should not have been written")
+		}
+	})
 }