test(19.3-06): wait for the queued site-cache purge before asserting (WR-01)

- every read of the purge receiver first drains the app's purger through
  cooler.SiteCachePurger.Wait, since cooler now queues purges after commit

site_cache_admin_test.go

@@ -1,6 +1,7 @@
 package faq_test
 
 import (
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -9,8 +10,10 @@ import (
 	"strings"
 	"sync"
 	"testing"
+	"time"
 
 	"git.golem15.com/golem15/sm-faq-plugin/models"
+	"git.golem15.com/golem15/summercms/modules/backpack"
 	"git.golem15.com/golem15/summercms/modules/cooler"
 )
 
@@ -37,6 +40,9 @@ type purgeReceiver struct {
 	got    []purgeRequest
 	status int
 	probe  func() string
+	// drain waits for the queued purges of the app under test; see
+	// drainFrom.
+	drain func()
 }
 
 func newPurgeReceiver(t *testing.T) *purgeReceiver {
@@ -67,6 +73,12 @@ func newPurgeReceiver(t *testing.T) *purgeReceiver {
 }
 
 func (r *purgeReceiver) take() []purgeRequest {
+	r.mu.Lock()
+	drain := r.drain
+	r.mu.Unlock()
+	if drain != nil {
+		drain()
+	}
 	r.mu.Lock()
 	defer r.mu.Unlock()
 	got := r.got
@@ -74,6 +86,21 @@ func (r *purgeReceiver) take() []purgeRequest {
 	return got
 }
 
+// drainFrom makes every read of r first wait for the purges queued on app's
+// site-cache purger: cooler queues them after commit and sends them in the
+// background, so a save's purge is asserted only once it was sent.
+func (r *purgeReceiver) drainFrom(t *testing.T, app *backpack.App) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.drain = func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		if err := cooler.SiteCacheFromApp(app).Wait(ctx); err != nil {
+			t.Errorf("waiting for the queued site-cache purge: %v", err)
+		}
+	}
+}
+
 func (r *purgeReceiver) setStatus(status int) {
 	r.mu.Lock()
 	r.status = status
@@ -114,6 +141,7 @@ func (r *purgeReceiver) expectOnePurge(t *testing.T, stage, slug string) purgeRe
 func TestFaqAdminPurgesSiteCache(t *testing.T) {
 	recv := newPurgeReceiver(t)
 	e := bootFAQ(t)
+	recv.drainFrom(t, e.app)
 	// SiteCacheFromApp reads the keys on the first save, so they can be set
 	// after boot.
 	if err := e.app.Config.Set(cooler.SiteCachePurgeURLKey, recv.srv.URL+purgeTestPath); err != nil {