test: a search engine out of its limit gives way to DuckDuckGo

internal/server/search_test.go

@@ -75,3 +75,23 @@ func TestSearchProviders(t *testing.T) {
 		t.Fatalf("fallback: %+v %v", rs, err)
 	}
 }
+
+// The chosen engine's limit spent (429 and the like): DuckDuckGo answers.
+func TestSearchLimitFallsBack(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, `{"error":"rate limit"}`, http.StatusTooManyRequests)
+	}))
+	defer srv.Close()
+	old := ddgSearch
+	defer func() { ddgSearch = old }()
+	ddgSearch = func(ctx context.Context, q string, n int) ([]searchResult, error) {
+		return []searchResult{{Title: "DDG " + q}}, nil
+	}
+	braveURL, tavilyURL = srv.URL, srv.URL
+	for _, e := range []string{"brave", "tavily", "searxng"} {
+		rs, err := searchWith(context.Background(), searchConf{Engine: e, Key: "k", URL: srv.URL}, "x", 6)
+		if err != nil || len(rs) != 1 || rs[0].Title != "DDG x" {
+			t.Fatalf("%s: %+v %v", e, rs, err)
+		}
+	}
+}