test: expand test coverage across diary, product, savedrecipe, ingredient, menu, recognition

- Fix locale_test: add TestMain to pre-populate Supported map so zh/es tests pass
- Export pure functions for testability: ResolveWeekStart, MapCuisineSlug (menu + savedrecipe), MergeAndDeduplicate
- Introduce repository interfaces (DiaryRepository, ProductRepository, SavedRecipeRepository, IngredientSearcher) in each handler; NewHandler now accepts interfaces — concrete *Repository still satisfies them
- Add mock files: diary/mocks, product/mocks, savedrecipe/mocks
- Add handler unit tests (no DB) for diary (8), product (8), savedrecipe (8), ingredient (5)
- Add pure-function unit tests: menu/ResolveWeekStart (6), savedrecipe/MapCuisineSlug (5), recognition/MergeAndDeduplicate (6)
- Add repository integration tests (//go:build integration): diary (4), product (6)
- Extend recipe integration tests: GetByID_Found, GetByID_WithTranslation

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/tests/ingredient/handler_test.go

@@ -0,0 +1,157 @@
+package ingredient_test
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/food-ai/backend/internal/domain/ingredient"
+	"github.com/food-ai/backend/internal/infra/middleware"
+	"github.com/go-chi/chi/v5"
+)
+
+// mockIngredientSearcher is an inline mock for ingredient.IngredientSearcher.
+type mockIngredientSearcher struct {
+	searchFn func(ctx context.Context, query string, limit int) ([]*ingredient.IngredientMapping, error)
+}
+
+func (m *mockIngredientSearcher) Search(ctx context.Context, query string, limit int) ([]*ingredient.IngredientMapping, error) {
+	return m.searchFn(ctx, query, limit)
+}
+
+type alwaysAuthValidator struct{ userID string }
+
+func (v *alwaysAuthValidator) ValidateAccessToken(_ string) (*middleware.TokenClaims, error) {
+	return &middleware.TokenClaims{UserID: v.userID}, nil
+}
+
+func buildRouter(handler *ingredient.Handler) *chi.Mux {
+	router := chi.NewRouter()
+	router.Use(middleware.Auth(&alwaysAuthValidator{userID: "user-1"}))
+	router.Get("/ingredients/search", handler.Search)
+	return router
+}
+
+func authorizedRequest(target string) *http.Request {
+	request := httptest.NewRequest(http.MethodGet, target, bytes.NewReader(nil))
+	request.Header.Set("Authorization", "Bearer test-token")
+	return request
+}
+
+func TestSearch_EmptyQuery_ReturnsEmptyArray(t *testing.T) {
+	// When q is empty, the handler returns [] without calling the repository.
+	handler := ingredient.NewHandler(&mockIngredientSearcher{})
+	router := buildRouter(handler)
+
+	recorder := httptest.NewRecorder()
+	router.ServeHTTP(recorder, authorizedRequest("/ingredients/search"))
+
+	if recorder.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", recorder.Code)
+	}
+	if body := recorder.Body.String(); body != "[]" {
+		t.Errorf("expected body [], got %q", body)
+	}
+}
+
+func TestSearch_LimitTooLarge_UsesDefault(t *testing.T) {
+	// When limit > 50, the handler ignores it and uses default 10.
+	calledLimit := 0
+	mockRepo := &mockIngredientSearcher{
+		searchFn: func(ctx context.Context, query string, limit int) ([]*ingredient.IngredientMapping, error) {
+			calledLimit = limit
+			return []*ingredient.IngredientMapping{}, nil
+		},
+	}
+	handler := ingredient.NewHandler(mockRepo)
+	router := buildRouter(handler)
+
+	recorder := httptest.NewRecorder()
+	router.ServeHTTP(recorder, authorizedRequest("/ingredients/search?q=apple&limit=100"))
+
+	if recorder.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", recorder.Code)
+	}
+	if calledLimit != 10 {
+		t.Errorf("expected repo called with limit=10 (default), got %d", calledLimit)
+	}
+}
+
+func TestSearch_DefaultLimit(t *testing.T) {
+	// When no limit is supplied, the handler uses default 10.
+	calledLimit := 0
+	mockRepo := &mockIngredientSearcher{
+		searchFn: func(ctx context.Context, query string, limit int) ([]*ingredient.IngredientMapping, error) {
+			calledLimit = limit
+			return []*ingredient.IngredientMapping{}, nil
+		},
+	}
+	handler := ingredient.NewHandler(mockRepo)
+	router := buildRouter(handler)
+
+	recorder := httptest.NewRecorder()
+	router.ServeHTTP(recorder, authorizedRequest("/ingredients/search?q=apple"))
+
+	if recorder.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", recorder.Code)
+	}
+	if calledLimit != 10 {
+		t.Errorf("expected default limit 10, got %d", calledLimit)
+	}
+}
+
+func TestSearch_ValidLimit(t *testing.T) {
+	// limit=25 is within range and should be forwarded as-is.
+	calledLimit := 0
+	mockRepo := &mockIngredientSearcher{
+		searchFn: func(ctx context.Context, query string, limit int) ([]*ingredient.IngredientMapping, error) {
+			calledLimit = limit
+			return []*ingredient.IngredientMapping{}, nil
+		},
+	}
+	handler := ingredient.NewHandler(mockRepo)
+	router := buildRouter(handler)
+
+	recorder := httptest.NewRecorder()
+	router.ServeHTTP(recorder, authorizedRequest("/ingredients/search?q=apple&limit=25"))
+
+	if recorder.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", recorder.Code)
+	}
+	if calledLimit != 25 {
+		t.Errorf("expected limit 25, got %d", calledLimit)
+	}
+}
+
+func TestSearch_Success(t *testing.T) {
+	mockRepo := &mockIngredientSearcher{
+		searchFn: func(ctx context.Context, query string, limit int) ([]*ingredient.IngredientMapping, error) {
+			return []*ingredient.IngredientMapping{
+				{ID: "ing-1", CanonicalName: "apple"},
+			}, nil
+		},
+	}
+	handler := ingredient.NewHandler(mockRepo)
+	router := buildRouter(handler)
+
+	recorder := httptest.NewRecorder()
+	router.ServeHTTP(recorder, authorizedRequest("/ingredients/search?q=apple"))
+
+	if recorder.Code != http.StatusOK {
+		t.Errorf("expected 200, got %d", recorder.Code)
+	}
+
+	var mappings []ingredient.IngredientMapping
+	if decodeError := json.NewDecoder(recorder.Body).Decode(&mappings); decodeError != nil {
+		t.Fatalf("decode response: %v", decodeError)
+	}
+	if len(mappings) != 1 {
+		t.Errorf("expected 1 result, got %d", len(mappings))
+	}
+	if mappings[0].CanonicalName != "apple" {
+		t.Errorf("expected canonical_name=apple, got %q", mappings[0].CanonicalName)
+	}
+}