syz-cluster: extend dashboard testing

Check a few more URLs.
Add a TODO about the problem around template error handling - if we
stream the output directly to w, we cannot set the 500 status if a
problem happens somewhere mid-template.

Author: a-nogikh

syz-cluster/dashboard/handler.go

@@ -393,6 +393,9 @@ func errToStatus(f func(http.ResponseWriter, *http.Request) error) http.HandlerF
 		} else if errors.Is(err, errBadRequest) {
 			http.Error(w, err.Error(), http.StatusBadRequest)
 		} else if err != nil {
+			// TODO: if the error happened in the template, likely we've already printed
+			// something to w. Unless we're in streamBlob(), it makes sense to first collect
+			// the output in some buffer and only dump it after the exit from the handler.
 			http.Error(w, err.Error(), http.StatusInternalServerError)
 		}
 	}

syz-cluster/dashboard/handler_test.go

@@ -26,7 +26,11 @@ func TestURLs(t *testing.T) {
 	handler, baseURL := testServer(t, env)
 	urlGen := api.NewURLGenerator(baseURL)
 
-	urls := []string{urlGen.Series(ids.SeriesID)}
+	urls := []string{
+		baseURL,
+		baseURL + "/stats",
+		urlGen.Series(ids.SeriesID),
+	}
 	for _, buildID := range []string{ids.BaseBuildID, ids.PatchedBuildID} {
 		urls = append(urls, urlGen.BuildConfig(buildID))
 		urls = append(urls, urlGen.BuildLog(buildID))