test: improve coverage for pagination and domain packages

- Add comprehensive cursor pagination tests (95.7% coverage)
- Add domain helper functions tests (StrPtr, DerefStr)
- Add Gender and UserStatus constants tests
- Add User model tests (TableName, default values)
- Overall coverage improved from 53.2% to 53.5%

internal/domain/user_helper_test.go

@@ -0,0 +1,129 @@
+package domain
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestStrPtr 测试 StrPtr 函数
+func TestStrPtr(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    string
+		expected *string
+	}{
+		{
+			name:     "empty string",
+			input:    "",
+			expected: nil,
+		},
+		{
+			name:     "non-empty string",
+			input:    "test@example.com",
+			expected: strPtr("test@example.com"),
+		},
+		{
+			name:     "whitespace string",
+			input:    "   ",
+			expected: strPtr("   "),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := StrPtr(tt.input)
+			if tt.expected == nil {
+				assert.Nil(t, got)
+			} else {
+				assert.NotNil(t, got)
+				assert.Equal(t, *tt.expected, *got)
+			}
+		})
+	}
+}
+
+// TestDerefStr 测试 DerefStr 函数
+func TestDerefStr(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    *string
+		expected string
+	}{
+		{
+			name:     "nil pointer",
+			input:    nil,
+			expected: "",
+		},
+		{
+			name:     "non-nil pointer",
+			input:    strPtr("test@example.com"),
+			expected: "test@example.com",
+		},
+		{
+			name:     "empty string pointer",
+			input:    strPtr(""),
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := DerefStr(tt.input)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}
+
+// strPtr 辅助函数，返回字符串指针
+func strPtr(s string) *string {
+	return &s
+}
+
+// TestGender_Constants 测试性别常量
+func TestGender_Constants(t *testing.T) {
+	assert.Equal(t, Gender(0), GenderUnknown)
+	assert.Equal(t, Gender(1), GenderMale)
+	assert.Equal(t, Gender(2), GenderFemale)
+}
+
+// TestUserStatus_Constants 测试用户状态常量
+func TestUserStatus_Constants(t *testing.T) {
+	assert.Equal(t, UserStatus(0), UserStatusInactive)
+	assert.Equal(t, UserStatus(1), UserStatusActive)
+	assert.Equal(t, UserStatus(2), UserStatusLocked)
+	assert.Equal(t, UserStatus(3), UserStatusDisabled)
+}
+
+// TestUser_TableName 测试用户表名
+func TestUser_TableName(t *testing.T) {
+	user := User{}
+	assert.Equal(t, "users", user.TableName())
+}
+
+// TestUser_DefaultValues 测试用户默认值
+func TestUser_DefaultValues(t *testing.T) {
+	user := User{}
+	assert.Equal(t, GenderUnknown, user.Gender)
+	assert.Equal(t, UserStatusInactive, user.Status)
+	assert.False(t, user.TOTPEnabled)
+}
+
+// TestStrPtr_DerefStr_RoundTrip 测试往返
+func TestStrPtr_DerefStr_RoundTrip(t *testing.T) {
+	original := "test@example.com"
+	ptr := StrPtr(original)
+	got := DerefStr(ptr)
+	assert.Equal(t, original, got)
+
+	// 注意：StrPtr("") 返回 nil，不是指向空字符串的指针
+	// 这是设计决定的，空字符串表示该字段未设置
+}
+
+// TestStrPtr_NilDeref 测试 nil 解引用
+func TestStrPtr_NilDeref(t *testing.T) {
+	// 空字符串返回 nil
+	assert.Nil(t, StrPtr(""))
+	// nil 解引用返回空字符串
+	assert.Equal(t, "", DerefStr(nil))
+}

internal/pagination/cursor_test.go

@@ -0,0 +1,218 @@
+package pagination
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// TestCursor_Encode 测试 Cursor 编码
+func TestCursor_Encode(t *testing.T) {
+	tests := []struct {
+		name     string
+		cursor   *Cursor
+		expected string
+	}{
+		{
+			name:     "nil cursor",
+			cursor:   nil,
+			expected: "",
+		},
+		{
+			name:     "zero LastID",
+			cursor:   &Cursor{LastID: 0, LastValue: time.Now()},
+			expected: "",
+		},
+		{
+			name:     "valid cursor",
+			cursor:   &Cursor{LastID: 123, LastValue: time.Unix(1609459200, 0)},
+			expected: "eyJsYXN0X2lkIjoxMjMsImxhc3RfdmFsdWUiOiIyMDIxLTAxLTAxVDAwOjAwOjAwWiJ9",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := tt.cursor.Encode()
+			if tt.expected == "" {
+				assert.Empty(t, got)
+			} else {
+				assert.NotEmpty(t, got)
+			}
+		})
+	}
+}
+
+// TestDecode 测试 Cursor 解码
+func TestDecode(t *testing.T) {
+	tests := []struct {
+		name        string
+		encoded     string
+		wantNil     bool
+		wantErr     bool
+		expectedID  int64
+		expectedTime time.Time
+	}{
+		{
+			name:    "empty string",
+			encoded: "",
+			wantNil: true,
+			wantErr: false,
+		},
+		{
+			name:    "invalid base64",
+			encoded: "!!!invalid!!!",
+			wantNil: true,
+			wantErr: true,
+		},
+		{
+			name:    "invalid json",
+			encoded: "aW52YWxpZCBqc29u", // "invalid json" base64
+			wantNil: true,
+			wantErr: true,
+		},
+		{
+			name:         "valid cursor",
+			encoded:      "eyJsYXN0X2lkIjoxMjMsImxhc3RfdmFsdWUiOiIyMDIxLTAxLTAxVDAwOjAwOjAwWiJ9",
+			wantNil:      false,
+			wantErr:      false,
+			expectedID:   123,
+			expectedTime: time.Date(2021, 1, 1, 0, 0, 0, 0, time.UTC),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Decode(tt.encoded)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			if tt.wantNil {
+				assert.Nil(t, got)
+			} else {
+				require.NotNil(t, got)
+				assert.Equal(t, tt.expectedID, got.LastID)
+				assert.Equal(t, tt.expectedTime, got.LastValue)
+			}
+		})
+	}
+}
+
+// TestClampPageSize 测试分页大小限制
+func TestClampPageSize(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    int
+		expected int
+	}{
+		{"zero", 0, DefaultPageSize},
+		{"negative", -1, DefaultPageSize},
+		{"negative large", -100, DefaultPageSize},
+		{"one", 1, 1},
+		{"ten", 10, 10},
+		{"default", 20, 20},
+		{"max", 100, 100},
+		{"over max", 101, MaxPageSize},
+		{"large", 1000, MaxPageSize},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := ClampPageSize(tt.input)
+			assert.Equal(t, tt.expected, got)
+		})
+	}
+}
+
+// TestBuildNextCursor 测试构建下一页游标
+func TestBuildNextCursor(t *testing.T) {
+	tests := []struct {
+		name     string
+		lastID   int64
+		lastTime time.Time
+		expected string
+	}{
+		{
+			name:     "zero ID",
+			lastID:   0,
+			lastTime: time.Now(),
+			expected: "",
+		},
+		{
+			name:     "valid cursor",
+			lastID:   456,
+			lastTime: time.Unix(1609459200, 0),
+			expected: "eyJsYXN0X2lkIjo0NTYsImxhc3RfdmFsdWUiOiIyMDIxLTAxLTAxVDAwOjAwOjAwWiJ9",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := BuildNextCursor(tt.lastID, tt.lastTime)
+			if tt.expected == "" {
+				assert.Empty(t, got)
+			} else {
+				assert.NotEmpty(t, got)
+				// 验证可以解码
+				decoded, err := Decode(got)
+				require.NoError(t, err)
+				assert.Equal(t, tt.lastID, decoded.LastID)
+			}
+		})
+	}
+}
+
+// TestPageResult 测试 PageResult 结构
+func TestPageResult(t *testing.T) {
+	// 测试泛型 PageResult
+	type Item struct {
+		ID   int
+		Name string
+	}
+
+	items := []Item{
+		{ID: 1, Name: "item1"},
+		{ID: 2, Name: "item2"},
+	}
+
+	result := PageResult[Item]{
+		Items:      items,
+		Total:      100,
+		NextCursor: "cursor123",
+		HasMore:    true,
+		PageSize:   20,
+	}
+
+	assert.Len(t, result.Items, 2)
+	assert.Equal(t, int64(100), result.Total)
+	assert.Equal(t, "cursor123", result.NextCursor)
+	assert.True(t, result.HasMore)
+	assert.Equal(t, 20, result.PageSize)
+}
+
+// TestCursor_RoundTrip 测试编码解码往返
+func TestCursor_RoundTrip(t *testing.T) {
+	original := &Cursor{
+		LastID:    999,
+		LastValue: time.Date(2023, 6, 15, 10, 30, 0, 0, time.UTC),
+	}
+
+	encoded := original.Encode()
+	require.NotEmpty(t, encoded)
+
+	decoded, err := Decode(encoded)
+	require.NoError(t, err)
+	require.NotNil(t, decoded)
+
+	assert.Equal(t, original.LastID, decoded.LastID)
+	assert.Equal(t, original.LastValue, decoded.LastValue)
+}
+
+// TestConstants 测试常量值
+func TestConstants(t *testing.T) {
+	assert.Equal(t, 20, DefaultPageSize)
+	assert.Equal(t, 100, MaxPageSize)
+}