test: add comprehensive test coverage and improve code quality

- Add new test files for auth, service, and handler modules
- Improve test organization and coverage
- Refactor code for better maintainability
- Add captcha, settings, stats, and theme handler tests
- Add auth module tests (CAS, OAuth, password, SSO, state)
- Add service layer tests for auth, export, permissions, roles
- All Go tests pass (exit code 0)
- All frontend tests pass (325 tests in 59 files)

internal/api/handler/captcha_handler_test.go

@@ -0,0 +1,146 @@
+package handler_test
+
+import (
+	"bytes"
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/gin-gonic/gin"
+	"github.com/user-management-system/internal/api/handler"
+	"github.com/user-management-system/internal/cache"
+	"github.com/user-management-system/internal/service"
+)
+
+// =============================================================================
+// Captcha Handler Tests - TDD approach
+// =============================================================================
+
+func TestCaptchaHandler_GenerateCaptcha(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	l1Cache := cache.NewL1Cache()
+	l2Cache := cache.NewRedisCache(false)
+	cacheManager := cache.NewCacheManager(l1Cache, l2Cache)
+	captchaSvc := service.NewCaptchaService(cacheManager)
+	h := handler.NewCaptchaHandler(captchaSvc)
+
+	t.Run("生成验证码成功", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Request = httptest.NewRequest("GET", "/api/v1/captcha/generate", nil)
+
+		h.GenerateCaptcha(c)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("期望状态码 %d, 得到 %d", http.StatusOK, w.Code)
+		}
+
+		var resp map[string]interface{}
+		if err := json.Unmarshal(w.Body.Bytes(), &resp); err != nil {
+			t.Fatalf("解析响应失败: %v", err)
+		}
+
+		if resp["code"].(float64) != 0 {
+			t.Errorf("期望 code=0, 得到 %v", resp["code"])
+		}
+
+		data := resp["data"].(map[string]interface{})
+		if data["captcha_id"] == "" {
+			t.Error("captcha_id 不应为空")
+		}
+		if data["image"] == "" {
+			t.Error("image 不应为空")
+		}
+	})
+}
+
+func TestCaptchaHandler_VerifyCaptcha(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	l1Cache := cache.NewL1Cache()
+	l2Cache := cache.NewRedisCache(false)
+	cacheManager := cache.NewCacheManager(l1Cache, l2Cache)
+	captchaSvc := service.NewCaptchaService(cacheManager)
+	h := handler.NewCaptchaHandler(captchaSvc)
+
+	t.Run("验证成功", func(t *testing.T) {
+		// 先生成验证码
+		result, _ := captchaSvc.Generate(nil)
+		// 从缓存获取答案
+		cachedVal, ok := cacheManager.Get(nil, "captcha:"+result.CaptchaID)
+		if !ok {
+			t.Fatal("验证码未存储到缓存")
+		}
+		answer := cachedVal.(string)
+
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		body := `{"captcha_id":"` + result.CaptchaID + `","answer":"` + answer + `"}`
+		c.Request = httptest.NewRequest("POST", "/api/v1/captcha/verify", nil)
+		c.Request.Body = io.NopCloser(bytes.NewReader([]byte(body)))
+		c.Request.Header.Set("Content-Type", "application/json")
+
+		h.VerifyCaptcha(c)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("期望状态码 %d, 得到 %d", http.StatusOK, w.Code)
+		}
+	})
+
+	t.Run("验证失败-错误答案", func(t *testing.T) {
+		result, _ := captchaSvc.Generate(nil)
+
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		body := `{"captcha_id":"` + result.CaptchaID + `","answer":"wrong"}`
+		c.Request = httptest.NewRequest("POST", "/api/v1/captcha/verify", nil)
+		c.Request.Body = io.NopCloser(bytes.NewReader([]byte(body)))
+		c.Request.Header.Set("Content-Type", "application/json")
+
+		h.VerifyCaptcha(c)
+
+		if w.Code != http.StatusBadRequest {
+			t.Errorf("期望状态码 %d, 得到 %d", http.StatusBadRequest, w.Code)
+		}
+	})
+
+	t.Run("验证失败-缺少参数", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		body := `{"captcha_id":""}`
+		c.Request = httptest.NewRequest("POST", "/api/v1/captcha/verify", nil)
+		c.Request.Body = io.NopCloser(bytes.NewReader([]byte(body)))
+		c.Request.Header.Set("Content-Type", "application/json")
+
+		h.VerifyCaptcha(c)
+
+		if w.Code != http.StatusBadRequest {
+			t.Errorf("期望状态码 %d, 得到 %d", http.StatusBadRequest, w.Code)
+		}
+	})
+}
+
+func TestCaptchaHandler_GetCaptchaImage(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	l1Cache := cache.NewL1Cache()
+	l2Cache := cache.NewRedisCache(false)
+	cacheManager := cache.NewCacheManager(l1Cache, l2Cache)
+	captchaSvc := service.NewCaptchaService(cacheManager)
+	h := handler.NewCaptchaHandler(captchaSvc)
+
+	t.Run("获取验证码图片", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Request = httptest.NewRequest("GET", "/api/v1/captcha/image?captcha_id=test", nil)
+
+		h.GetCaptchaImage(c)
+
+		if w.Code != http.StatusOK {
+			t.Errorf("期望状态码 %d, 得到 %d", http.StatusOK, w.Code)
+		}
+	})
+}