Add test for converting saved filter ids to list ids and vice versa

pkg/models/saved_filters.go

@@ -62,16 +62,20 @@ func (s *SavedFilter) getTaskCollection() *TaskCollection {
 func getSavedFilterIDFromListID(listID int64) (filterID int64) {
 	// We get the id of the saved filter by multiplying the ListID with -1 and subtracting one
 	filterID = listID*-1 - 1
-	if filterID > 0 {
+	// FilterIDs from listIDs are always positive
+	if filterID < 0 {
 		filterID = 0
 	}
 	return
 }
 
 func getListIDFromSavedFilterID(filterID int64) (listID int64) {
-	// Since both ways work the same way, we can just call the other function here.
-	// Might change in the future though.
-	return getSavedFilterIDFromListID(filterID)
+	listID = filterID*-1 - 1
+	// ListIDs from saved filters are always negative
+	if listID > 0 {
+		listID = 0
+	}
+	return
 }
 
 func getSavedFiltersForUser(auth web.Auth) (filters []*SavedFilter, err error) {

pkg/models/saved_filters_test.go

@@ -0,0 +1,40 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-2020 Vikunja and contributors. All rights reserved.
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package models
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestSavedFilter_getListIDFromFilter(t *testing.T) {
+	t.Run("normal", func(t *testing.T) {
+		assert.Equal(t, int64(-2), getListIDFromSavedFilterID(1))
+	})
+	t.Run("invalid", func(t *testing.T) {
+		assert.Equal(t, int64(0), getListIDFromSavedFilterID(-1))
+	})
+}
+
+func TestSavedFilter_getFilterIDFromListID(t *testing.T) {
+	t.Run("normal", func(t *testing.T) {
+		assert.Equal(t, int64(1), getSavedFilterIDFromListID(-2))
+	})
+	t.Run("invalid", func(t *testing.T) {
+		assert.Equal(t, int64(0), getSavedFilterIDFromListID(2))
+	})
+}