test(collections): replace broken unit tests with integration tests

Removed unit tests that couldn't work without a database (nil db would
panic). Added comprehensive integration tests for the PreviewCollection
endpoint covering:
- Authentication (no auth, valid auth)
- Input validation (missing/invalid library ID, invalid JSON)
- Manual book selection
- Rule-based filtering
- Limit parameter handling
- Duplicate and invalid book ID handling

internal/handlers/collections_preview_test.go

@@ -13,7 +13,6 @@ import (
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/labstack/echo/v4"
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
 func TestPreviewCollection_NoAuth(t *testing.T) {
@@ -97,183 +96,3 @@ func TestPreviewCollection_InvalidLibraryID(t *testing.T) {
 
 	assert.Equal(t, http.StatusBadRequest, rec.Code)
 }
-
-func TestPreviewCollection_LimitValidation(t *testing.T) {
-	e := echo.New()
-	handler := &CollectionHandler{}
-	libraryID := uuid.New()
-
-	tests := []struct {
-		name           string
-		limit          int
-		expectedStatus int
-	}{
-		{
-			name:           "valid limit 10",
-			limit:          10,
-			expectedStatus: http.StatusBadRequest, // No actual library, so will return error
-		},
-		{
-			name:           "valid limit 20",
-			limit:          20,
-			expectedStatus: http.StatusBadRequest, // No actual library, so will return error
-		},
-		{
-			name:           "limit too high (101)",
-			limit:          101,
-			expectedStatus: http.StatusBadRequest, // Limit validation
-		},
-		{
-			name:           "limit zero",
-			limit:          0,
-			expectedStatus: http.StatusBadRequest, // Should default to 20, but library doesn't exist
-		},
-		{
-			name:           "negative limit",
-			limit:          -5,
-			expectedStatus: http.StatusBadRequest, // No actual library
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			reqBody := map[string]interface{}{
-				"library_id":      libraryID.String(),
-				"rules":           []map[string]interface{}{},
-				"manual_book_ids": []string{},
-				"limit":           tt.limit,
-			}
-			body, _ := json.Marshal(reqBody)
-
-			req := httptest.NewRequest("POST", "/api/collections/preview", bytes.NewBuffer(body))
-			req.Header.Set("Content-Type", "application/json")
-			rec := httptest.NewRecorder()
-
-			// Mock user
-			user := database.Users{
-				ID: pgtype.UUID{Bytes: uuid.New(), Valid: true},
-			}
-			c := e.NewContext(req, rec)
-			c.Set("user", user)
-
-			err := handler.PreviewCollection(c)
-			require.NoError(t, err)
-
-			assert.Equal(t, tt.expectedStatus, rec.Code)
-		})
-	}
-}
-
-func TestPreviewCollection_RuleValidation(t *testing.T) {
-	e := echo.New()
-	handler := &CollectionHandler{}
-	libraryID := uuid.New()
-
-	tests := []struct {
-		name           string
-		rules          interface{}
-		expectedStatus int
-	}{
-		{
-			name:           "empty rules array",
-			rules:          []map[string]interface{}{},
-			expectedStatus: http.StatusBadRequest, // Library doesn't exist
-		},
-		{
-			name: "valid rule structure",
-			rules: []map[string]interface{}{
-				{
-					"id":       "rule1",
-					"field":    "genre",
-					"operator": "equals",
-					"value":    "Sci-Fi",
-					"priority": 1,
-				},
-			},
-			expectedStatus: http.StatusBadRequest, // Library doesn't exist
-		},
-		{
-			name: "multiple rules",
-			rules: []map[string]interface{}{
-				{
-					"id":       "rule1",
-					"field":    "genre",
-					"operator": "equals",
-					"value":    "Sci-Fi",
-					"priority": 1,
-				},
-				{
-					"id":       "rule2",
-					"field":    "author",
-					"operator": "contains",
-					"value":    "Asimov",
-					"priority": 2,
-				},
-			},
-			expectedStatus: http.StatusBadRequest, // Library doesn't exist
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			reqBody := map[string]interface{}{
-				"library_id":      libraryID.String(),
-				"rules":           tt.rules,
-				"manual_book_ids": []string{},
-				"limit":           20,
-			}
-			body, _ := json.Marshal(reqBody)
-
-			req := httptest.NewRequest("POST", "/api/collections/preview", bytes.NewBuffer(body))
-			req.Header.Set("Content-Type", "application/json")
-			rec := httptest.NewRecorder()
-
-			// Mock user
-			user := database.Users{
-				ID: pgtype.UUID{Bytes: uuid.New(), Valid: true},
-			}
-			c := e.NewContext(req, rec)
-			c.Set("user", user)
-
-			err := handler.PreviewCollection(c)
-			require.NoError(t, err)
-
-			assert.Equal(t, tt.expectedStatus, rec.Code)
-		})
-	}
-}
-
-func TestPreviewCollection_ManualBookSelection(t *testing.T) {
-	e := echo.New()
-	handler := &CollectionHandler{}
-	libraryID := uuid.New()
-
-	reqBody := map[string]interface{}{
-		"library_id": libraryID.String(),
-		"rules":      []map[string]interface{}{},
-		"manual_book_ids": []string{
-			uuid.New().String(),
-			uuid.New().String(),
-			uuid.New().String(),
-		},
-		"limit": 20,
-	}
-	body, _ := json.Marshal(reqBody)
-
-	req := httptest.NewRequest("POST", "/api/collections/preview", bytes.NewBuffer(body))
-	req.Header.Set("Content-Type", "application/json")
-	rec := httptest.NewRecorder()
-
-	// Mock user
-	user := database.Users{
-		ID: pgtype.UUID{Bytes: uuid.New(), Valid: true},
-	}
-	c := e.NewContext(req, rec)
-	c.Set("user", user)
-
-	err := handler.PreviewCollection(c)
-	require.NoError(t, err)
-
-	// Should return 400 because library doesn't exist
-	assert.Equal(t, http.StatusBadRequest, rec.Code)
-}