test: add comprehensive test coverage for dashboard

Phase 11 - Unit and Integration Tests

Service Layer Tests (dashboard_service_test.go):
- Test filterHiddenCollections with multiple scenarios
- Test reorderCollections with custom orders
- Test sortByPriority sorting logic
- All 6 tests passing

Handler Tests (dashboard_test.go):
- Test BuildSections type conversion
- Test textToString helper function
- Test getViewAllURL mapping
- All 7 tests passing

Preview Tests (collections_preview_test.go):
- Test preview endpoint validation
- Test limit validation
- Test rule validation
- 6 test scenarios

Integration Tests (dashboard_integration_test.go):
- Test GET /api/dashboard/sections end-to-end
- Test PUT /api/dashboard/preferences
- Test POST /api/dashboard/restore-system-collection
- Test authentication and validation
- 9 test scenarios total

Part of Carousel Dashboard Plan completion

internal/handlers/dashboard_test.go

@@ -0,0 +1,182 @@
+package handlers
+
+import (
+	"testing"
+
+	"bookhoard/internal/database"
+	"bookhoard/internal/services"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgtype"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestBuildSections_ConvertsServiceTypesToHandlerTypes(t *testing.T) {
+	itemUUID := uuid.New()
+
+	serviceSections := []services.DashboardSection{
+		{
+			CollectionID:   uuid.UUID{},
+			CollectionName: "continue-reading",
+			QueryType:      "continue-reading",
+			Priority:       1,
+			IsSystem:       true,
+			Title:          "Continue Reading",
+			Description:    "Books you're currently reading",
+			Icon:           "📖",
+			Items: []database.MediaItems{
+				{
+					ID:             pgtype.UUID{Bytes: itemUUID, Valid: true},
+					Title:          "Test Book",
+					Author:         pgtype.Text{String: "Test Author", Valid: true},
+					CoverImagePath: pgtype.Text{String: "/path/to/cover.jpg", Valid: true},
+				},
+			},
+		},
+		{
+			CollectionID:   uuid.UUID{},
+			CollectionName: "my-favorites",
+			QueryType:      "filter",
+			Priority:       10,
+			IsSystem:       false,
+			Title:          "My Favorites",
+			Description:    "My favorite books",
+			Icon:           "⭐",
+			Items:          []database.MediaItems{},
+		},
+	}
+
+	result := BuildSections(serviceSections)
+
+	assert.Equal(t, 2, len(result), "should have 2 sections")
+
+	section1 := result[0]
+	assert.Equal(t, "continue-reading", section1.ID, "ID should match")
+	assert.True(t, section1.IsSystem, "IsSystem should be boolean true")
+	assert.Equal(t, "Continue Reading", section1.Title, "Title should be string")
+	assert.Equal(t, "Books you're currently reading", section1.Description, "Description should be string")
+	assert.Equal(t, "📖", section1.Icon, "Icon should be string")
+	assert.Equal(t, 1, section1.Priority, "Priority should be number")
+	assert.Equal(t, "/section/continue-reading", section1.ViewAllURL, "ViewAllURL should match system collection")
+
+	section2 := result[1]
+	assert.Equal(t, "my-favorites", section2.ID)
+	assert.False(t, section2.IsSystem, "IsSystem should be boolean false")
+	assert.Equal(t, "My Favorites", section2.Title)
+	assert.Equal(t, "", section2.ViewAllURL, "ViewAllURL should be empty for user collections")
+}
+
+func TestBuildSections_ConvertsItemsCorrectly(t *testing.T) {
+	itemUUID := uuid.New()
+
+	serviceSections := []services.DashboardSection{
+		{
+			CollectionID:   uuid.UUID{},
+			CollectionName: "continue-reading",
+			QueryType:      "continue-reading",
+			Priority:       1,
+			IsSystem:       true,
+			Title:          "Continue Reading",
+			Description:    "Books you're currently reading",
+			Icon:           "📖",
+			Items: []database.MediaItems{
+				{
+					ID:             pgtype.UUID{Bytes: itemUUID, Valid: true},
+					Title:          "Test Book",
+					Author:         pgtype.Text{String: "Test Author", Valid: true},
+					CoverImagePath: pgtype.Text{String: "/path/to/cover.jpg", Valid: true},
+				},
+			},
+		},
+	}
+
+	result := BuildSections(serviceSections)
+
+	assert.Equal(t, 1, len(result), "should have 1 section")
+	section := result[0]
+	assert.Equal(t, 1, len(section.Items), "should have 1 item")
+
+	item := section.Items[0]
+	assert.Equal(t, itemUUID.String(), item.MediaItemID, "MediaItemID should match")
+	assert.Equal(t, "Test Book", item.Title, "Title should be string")
+	assert.Equal(t, "Test Author", item.Author, "Author should be string")
+	assert.Equal(t, "/path/to/cover.jpg", item.CoverImagePath, "CoverImagePath should be string")
+}
+
+func TestTextToString_Valid(t *testing.T) {
+	tests := []struct {
+		name     string
+		input    pgtype.Text
+		expected string
+	}{
+		{
+			name:     "valid text",
+			input:    pgtype.Text{String: "hello", Valid: true},
+			expected: "hello",
+		},
+		{
+			name:     "empty text",
+			input:    pgtype.Text{String: "", Valid: true},
+			expected: "",
+		},
+		{
+			name:     "invalid text",
+			input:    pgtype.Text{String: "ignored", Valid: false},
+			expected: "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := textToString(tt.input)
+			assert.Equal(t, tt.expected, result, "textToString result mismatch")
+		})
+	}
+}
+
+func TestGetViewAllURL_SystemCollections(t *testing.T) {
+	tests := []struct {
+		name           string
+		collectionName string
+		queryType      string
+		expected       string
+	}{
+		{
+			name:           "continue-reading",
+			collectionName: "continue-reading",
+			queryType:      "continue-reading",
+			expected:       "/section/continue-reading",
+		},
+		{
+			name:           "recently-added",
+			collectionName: "recently-added",
+			queryType:      "recently-added",
+			expected:       "/section/recently-added",
+		},
+		{
+			name:           "recently-read",
+			collectionName: "recently-read",
+			queryType:      "recently-read",
+			expected:       "/history",
+		},
+		{
+			name:           "not-started",
+			collectionName: "not-started",
+			queryType:      "not-started",
+			expected:       "/section/not-started",
+		},
+		{
+			name:           "user collection",
+			collectionName: "my-favorites",
+			queryType:      "filter",
+			expected:       "",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := getViewAllURL(tt.collectionName, tt.queryType)
+			assert.Equal(t, tt.expected, result, "getViewAllURL mismatch")
+		})
+	}
+}