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

classes/site_cache_test.go

@@ -11,6 +11,7 @@ import (
 	"strings"
 	"sync"
 	"testing"
+	"time"
 )
 
 const (
@@ -206,10 +207,16 @@ func TestSiteCachePurgeRequest(t *testing.T) {
 		}
 	})
 
-	t.Run("outside a transaction the after-commit purge runs at once", func(t *testing.T) {
+	t.Run("outside a transaction the after-commit purge is queued at once", func(t *testing.T) {
 		captureLogs(t)
 		srv, hits := purgeReceiver(t, func(w http.ResponseWriter, _ *http.Request) { _, _ = w.Write([]byte(`{"purged":2}`)) })
-		PurgeSiteCacheAfterCommit(context.Background(), nil, newTestPurger(t, srv), "category", "now")
+		p := newTestPurger(t, srv)
+		PurgeSiteCacheAfterCommit(context.Background(), nil, p, "category", "now")
+		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+		defer cancel()
+		if err := p.Wait(ctx); err != nil {
+			t.Fatalf("Wait: %v", err)
+		}
 		if got := hits(); len(got) != 1 || got[0].body["kind"] != "category" || got[0].body["slug"] != "now" {
 			t.Fatalf("requests = %#v, want one", got)
 		}