test(dashboard): add unit tests for user-breakdown API

Handler tests (9 cases): group_id/model/endpoint filters, default
endpoint_type, custom limit, limit clamping, response format,
empty result, no-filter pass-through.

Repository test: resolveEndpointColumn mapping for inbound/upstream/path.

backend/internal/handler/admin/dashboard_handler_user_breakdown_test.go

+package admin
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/Wei-Shaw/sub2api/internal/pkg/usagestats"
+	"github.com/Wei-Shaw/sub2api/internal/service"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/require"
+)
+
+// --- mock repo ---
+
+type userBreakdownRepoCapture struct {
+	service.UsageLogRepository
+	capturedDim   usagestats.UserBreakdownDimension
+	capturedLimit int
+	result        []usagestats.UserBreakdownItem
+}
+
+func (r *userBreakdownRepoCapture) GetUserBreakdownStats(
+	_ context.Context, _, _ time.Time,
+	dim usagestats.UserBreakdownDimension, limit int,
+) ([]usagestats.UserBreakdownItem, error) {
+	r.capturedDim = dim
+	r.capturedLimit = limit
+	if r.result != nil {
+		return r.result, nil
+	}
+	return []usagestats.UserBreakdownItem{}, nil
+}
+
+func newUserBreakdownRouter(repo *userBreakdownRepoCapture) *gin.Engine {
+	gin.SetMode(gin.TestMode)
+	svc := service.NewDashboardService(repo, nil, nil, nil)
+	h := NewDashboardHandler(svc, nil)
+	router := gin.New()
+	router.GET("/admin/dashboard/user-breakdown", h.GetUserBreakdown)
+	return router
+}
+
+// --- tests ---
+
+func TestGetUserBreakdown_GroupIDFilter(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&group_id=42", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, int64(42), repo.capturedDim.GroupID)
+	require.Empty(t, repo.capturedDim.Model)
+	require.Empty(t, repo.capturedDim.Endpoint)
+	require.Equal(t, 50, repo.capturedLimit) // default limit
+}
+
+func TestGetUserBreakdown_ModelFilter(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&model=claude-opus-4-6", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, "claude-opus-4-6", repo.capturedDim.Model)
+	require.Equal(t, int64(0), repo.capturedDim.GroupID)
+}
+
+func TestGetUserBreakdown_EndpointFilter(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&endpoint=/v1/messages&endpoint_type=upstream", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, "/v1/messages", repo.capturedDim.Endpoint)
+	require.Equal(t, "upstream", repo.capturedDim.EndpointType)
+}
+
+func TestGetUserBreakdown_DefaultEndpointType(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&endpoint=/chat", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, "inbound", repo.capturedDim.EndpointType)
+}
+
+func TestGetUserBreakdown_CustomLimit(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&model=test&limit=100", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, 100, repo.capturedLimit)
+}
+
+func TestGetUserBreakdown_LimitClamped(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	// limit > 200 should fall back to default 50
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&model=test&limit=999", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, 50, repo.capturedLimit)
+}
+
+func TestGetUserBreakdown_ResponseFormat(t *testing.T) {
+	repo := &userBreakdownRepoCapture{
+		result: []usagestats.UserBreakdownItem{
+			{UserID: 1, Email: "alice@test.com", Requests: 100, TotalTokens: 50000, Cost: 1.5, ActualCost: 1.2},
+			{UserID: 2, Email: "bob@test.com", Requests: 50, TotalTokens: 25000, Cost: 0.8, ActualCost: 0.6},
+		},
+	}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&group_id=1", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+
+	var resp struct {
+		Code int `json:"code"`
+		Data struct {
+			Users     []usagestats.UserBreakdownItem `json:"users"`
+			StartDate string                         `json:"start_date"`
+			EndDate   string                         `json:"end_date"`
+		} `json:"data"`
+	}
+	err := json.Unmarshal(w.Body.Bytes(), &resp)
+	require.NoError(t, err)
+	require.Equal(t, 0, resp.Code)
+	require.Len(t, resp.Data.Users, 2)
+	require.Equal(t, int64(1), resp.Data.Users[0].UserID)
+	require.Equal(t, "alice@test.com", resp.Data.Users[0].Email)
+	require.Equal(t, int64(100), resp.Data.Users[0].Requests)
+	require.InDelta(t, 1.2, resp.Data.Users[0].ActualCost, 0.001)
+	require.Equal(t, "2026-03-01", resp.Data.StartDate)
+	require.Equal(t, "2026-03-16", resp.Data.EndDate)
+}
+
+func TestGetUserBreakdown_EmptyResult(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16&group_id=999", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+
+	var resp struct {
+		Data struct {
+			Users []usagestats.UserBreakdownItem `json:"users"`
+		} `json:"data"`
+	}
+	err := json.Unmarshal(w.Body.Bytes(), &resp)
+	require.NoError(t, err)
+	require.Empty(t, resp.Data.Users)
+}
+
+func TestGetUserBreakdown_NoFilters(t *testing.T) {
+	repo := &userBreakdownRepoCapture{}
+	router := newUserBreakdownRouter(repo)
+
+	req := httptest.NewRequest(http.MethodGet,
+		"/admin/dashboard/user-breakdown?start_date=2026-03-01&end_date=2026-03-16", nil)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, req)
+
+	require.Equal(t, http.StatusOK, w.Code)
+	require.Equal(t, int64(0), repo.capturedDim.GroupID)
+	require.Empty(t, repo.capturedDim.Model)
+	require.Empty(t, repo.capturedDim.Endpoint)
+}

backend/internal/repository/usage_log_repo_breakdown_test.go

+//go:build unit
+
+package repository
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestResolveEndpointColumn(t *testing.T) {
+	tests := []struct {
+		endpointType string
+		want         string
+	}{
+		{"inbound", "ul.inbound_endpoint"},
+		{"upstream", "ul.upstream_endpoint"},
+		{"path", "ul.inbound_endpoint || ' -> ' || ul.upstream_endpoint"},
+		{"", "ul.inbound_endpoint"},           // default
+		{"unknown", "ul.inbound_endpoint"},     // fallback
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.endpointType, func(t *testing.T) {
+			got := resolveEndpointColumn(tc.endpointType)
+			require.Equal(t, tc.want, got)
+		})
+	}
+}