Add local self-test flow and fix fallback regressions

backend/services/gemini_test.go

@@ -0,0 +1,41 @@
+package services
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+)
+
+func TestTranslateQueryFallsBackToGoogleWithoutGeminiKey(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`[[["rainy city street","비 오는 도시 거리",null,null,1]],null,"ko"]`))
+	}))
+	defer server.Close()
+
+	service := NewGeminiService("")
+	service.Client = &http.Client{Timeout: 2 * time.Second}
+	service.TranslateEndpoint = server.URL
+
+	translated := service.TranslateQuery("비 오는 도시 거리")
+	if translated != "rainy city street" {
+		t.Fatalf("expected google fallback translation, got %q", translated)
+	}
+}
+
+func TestTranslateQueryFallsBackToDictionaryWhenTranslateFails(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		http.Error(w, "boom", http.StatusBadGateway)
+	}))
+	defer server.Close()
+
+	service := NewGeminiService("")
+	service.Client = &http.Client{Timeout: 2 * time.Second}
+	service.TranslateEndpoint = server.URL
+
+	translated := service.TranslateQuery("숲속 커플")
+	if translated != "forest couple" {
+		t.Fatalf("expected dictionary fallback translation, got %q", translated)
+	}
+}