diff --git a/pkg/db/fixtures/task_relations.yml b/pkg/db/fixtures/task_relations.yml
index 750f2e217..4f852a7d2 100644
--- a/pkg/db/fixtures/task_relations.yml
+++ b/pkg/db/fixtures/task_relations.yml
@@ -34,3 +34,27 @@
   relation_kind: 'related'
   created_by_id: 1
   created: 2018-12-01 15:13:12
+- id: 7
+  task_id: 41
+  other_task_id: 43
+  relation_kind: 'subtask'
+  created_by_id: 15
+  created: 2018-12-01 15:13:12
+- id: 8
+  task_id: 43
+  other_task_id: 41
+  relation_kind: 'parenttask'
+  created_by_id: 15
+  created: 2018-12-01 15:13:12
+- id: 9
+  task_id: 41
+  other_task_id: 44
+  relation_kind: 'subtask'
+  created_by_id: 15
+  created: 2018-12-01 15:13:12
+- id: 10
+  task_id: 44
+  other_task_id: 41
+  relation_kind: 'parenttask'
+  created_by_id: 15
+  created: 2018-12-01 15:13:12
diff --git a/pkg/db/fixtures/tasks.yml b/pkg/db/fixtures/tasks.yml
index 77e11ae4d..7dc61a498 100644
--- a/pkg/db/fixtures/tasks.yml
+++ b/pkg/db/fixtures/tasks.yml
@@ -374,5 +374,61 @@
   due_date: 2023-03-01 15:00:00
   created: 2018-12-01 01:12:04
   updated: 2018-12-01 01:12:04
-  bucket_id: 1
+  bucket_id: 38
   position: 39
+- id: 41
+  uid: 'uid-caldav-test-parent-task'
+  title: 'Parent task for Caldav Test'
+  description: 'Description Caldav Test'
+  priority: 3
+  done: false
+  created_by_id: 15
+  project_id: 36
+  index: 40
+  due_date: 2023-03-01 15:00:00
+  created: 2018-12-01 01:12:04
+  updated: 2018-12-01 01:12:04
+  bucket_id: 38
+  position: 40
+- id: 42
+  uid: 'uid-caldav-test-parent-task-2'
+  title: 'Parent task for Caldav Test 2'
+  description: 'Description Caldav Test 2'
+  priority: 3
+  done: false
+  created_by_id: 15
+  project_id: 36
+  index: 41
+  due_date: 2023-03-01 15:00:00
+  created: 2018-12-01 01:12:04
+  updated: 2018-12-01 01:12:04
+  bucket_id: 38
+  position: 41
+- id: 43
+  uid: 'uid-caldav-test-child-task'
+  title: 'Child task for Caldav Test'
+  description: 'Description Caldav Test'
+  priority: 3
+  done: false
+  created_by_id: 15
+  project_id: 36
+  index: 42
+  due_date: 2023-03-01 15:00:00
+  created: 2018-12-01 01:12:04
+  updated: 2018-12-01 01:12:04
+  bucket_id: 38
+  position: 42
+- id: 44
+  uid: 'uid-caldav-test-child-task-2'
+  title: 'Child task for Caldav Test 2'
+  description: 'Description Caldav Test'
+  priority: 3
+  done: false
+  created_by_id: 15
+  project_id: 36
+  index: 43
+  due_date: 2023-03-01 15:00:00
+  created: 2018-12-01 01:12:04
+  updated: 2018-12-01 01:12:04
+  bucket_id: 38
+  position: 43
diff --git a/pkg/routes/caldav/listStorageProvider_test.go b/pkg/routes/caldav/listStorageProvider_test.go
new file mode 100644
index 000000000..a828a99af
--- /dev/null
+++ b/pkg/routes/caldav/listStorageProvider_test.go
@@ -0,0 +1,443 @@
+// Vikunja is a to-do list application to facilitate your life.
+// Copyright 2018-present 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 Affero General Public Licensee 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 Affero General Public Licensee for more details.
+//
+// You should have received a copy of the GNU Affero General Public Licensee
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package caldav
+
+// This file tests logic related to handling tasks in CALDAV format
+
+import (
+	"code.vikunja.io/api/pkg/db"
+	"code.vikunja.io/api/pkg/models"
+	"code.vikunja.io/api/pkg/user"
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+// Check logic related to creating sub-tasks
+func TestSubTask_Create(t *testing.T) {
+	u := &user.User{
+		ID:       15,
+		Username: "user15",
+		Email:    "user15@example.com",
+	}
+
+	//
+	// Create a subtask
+	//
+	t.Run("create", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		const taskUID = "uid_child1"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid_child1
+DTSTAMP:20230301T073337Z
+SUMMARY:Caldav child task 1
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task
+END:VTODO
+END:VCALENDAR`
+
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    &models.Task{UID: taskUID},
+			user:    u,
+		}
+
+		// Create the subtask:
+		taskResource, err := storage.CreateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Check that the result CALDAV contains the relation:
+		content, _ := taskResource.GetContentData()
+		assert.Contains(t, content, "UID:"+taskUID)
+		assert.Contains(t, content, "RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task")
+
+		// Get the task from the DB:
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+
+		// Check that the parent-child relationship is present:
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 1)
+		parentTask := task.RelatedTasks[models.RelationKindParenttask][0]
+		assert.Equal(t, "uid-caldav-test-parent-task", parentTask.UID)
+	})
+
+	//
+	// Create a subtask on a subtask, i.e. create a grand-child
+	//
+	t.Run("create grandchild on child task", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		const taskUID = "uid_child1"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid_child1
+DTSTAMP:20230301T073337Z
+SUMMARY:Caldav child task 1
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+RELATED-TO;RELTYPE=PARENT:uid-caldav-test-child-task
+END:VTODO
+END:VCALENDAR`
+
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    &models.Task{UID: taskUID},
+			user:    u,
+		}
+
+		// Create the task:
+		taskResource, err := storage.CreateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Check that the result CALDAV contains the relation:
+		content, _ := taskResource.GetContentData()
+		assert.Contains(t, content, "UID:"+taskUID)
+		assert.Contains(t, content, "RELATED-TO;RELTYPE=PARENT:uid-caldav-test-child-task")
+
+		// Get the task from the DB:
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+
+		// Check that the parent-child relationship of the grandchildren is present:
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 1)
+		parentTask := task.RelatedTasks[models.RelationKindParenttask][0]
+		assert.Equal(t, "uid-caldav-test-child-task", parentTask.UID)
+
+		// Get the child task and check that it now has a parent and a child:
+		tasks, err = models.GetTasksByUIDs(s, []string{"uid-caldav-test-child-task"}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 1)
+		parentTask = task.RelatedTasks[models.RelationKindParenttask][0]
+		assert.Equal(t, "uid-caldav-test-parent-task", parentTask.UID)
+		assert.Len(t, task.RelatedTasks[models.RelationKindSubtask], 1)
+		childTask := task.RelatedTasks[models.RelationKindSubtask][0]
+		assert.Equal(t, taskUID, childTask.UID)
+	})
+
+	//
+	// Create a subtask on a parent that we don't know anything about (yet)
+	//
+	t.Run("create subtask on unknown parent", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		// Create a subtask:
+		const taskUID = "uid_child1"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid_child1
+DTSTAMP:20230301T073337Z
+SUMMARY:Caldav child task 1
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-doesnt-exist-yet
+END:VTODO
+END:VCALENDAR`
+
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    &models.Task{UID: taskUID},
+			user:    u,
+		}
+
+		// Create the task:
+		taskResource, err := storage.CreateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Check that the result CALDAV contains the relation:
+		content, _ := taskResource.GetContentData()
+		assert.Contains(t, content, "UID:"+taskUID)
+		assert.Contains(t, content, "RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-doesnt-exist-yet")
+
+		// Get the task from the DB:
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+
+		// Check that the parent-child relationship is present:
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 1)
+		parentTask := task.RelatedTasks[models.RelationKindParenttask][0]
+		assert.Equal(t, "uid-caldav-test-parent-doesnt-exist-yet", parentTask.UID)
+
+		// Check that the non-existent parent task was created in the process:
+		tasks, err = models.GetTasksByUIDs(s, []string{"uid-caldav-test-parent-doesnt-exist-yet"}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+		assert.Equal(t, "uid-caldav-test-parent-doesnt-exist-yet", task.UID)
+	})
+}
+
+// Logic related to editing tasks and subtasks
+func TestSubTask_Edit(t *testing.T) {
+	u := &user.User{
+		ID:       15,
+		Username: "user15",
+		Email:    "user15@example.com",
+	}
+
+	//
+	// Edit a subtask and check that the relations are not gone
+	//
+	t.Run("edit subtask", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		// Edit the subtask:
+		const taskUID = "uid-caldav-test-child-task"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid-caldav-test-child-task
+DTSTAMP:20230301T073337Z
+SUMMARY:Child task for Caldav Test (edited)
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task
+END:VTODO
+END:VCALENDAR`
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    task,
+			user:    u,
+		}
+
+		// Edit the task:
+		taskResource, err := storage.UpdateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Check that the result CALDAV still contains the relation:
+		content, _ := taskResource.GetContentData()
+		assert.Contains(t, content, "UID:"+taskUID)
+		assert.Contains(t, content, "RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task")
+
+		// Get the task from the DB:
+		tasks, err = models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+
+		// Check that the parent-child relationship is still present:
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 1)
+		parentTask := task.RelatedTasks[models.RelationKindParenttask][0]
+		assert.Equal(t, "uid-caldav-test-parent-task", parentTask.UID)
+	})
+
+	//
+	// Edit a parent task and check that the subtasks are still linked
+	//
+	t.Run("edit parent", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		// Edit the parent task:
+		const taskUID = "uid-caldav-test-parent-task"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid-caldav-test-parent-task
+DTSTAMP:20230301T073337Z
+SUMMARY:Parent task for Caldav Test (edited)
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+END:VTODO
+END:VCALENDAR`
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    task,
+			user:    u,
+		}
+
+		// Edit the task:
+		_, err = storage.UpdateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Get the task from the DB:
+		tasks, err = models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+
+		// Check that the subtasks are still linked:
+		assert.Len(t, task.RelatedTasks[models.RelationKindSubtask], 2)
+		existingSubTask := task.RelatedTasks[models.RelationKindSubtask][0]
+		assert.Equal(t, "uid-caldav-test-child-task", existingSubTask.UID)
+		existingSubTask = task.RelatedTasks[models.RelationKindSubtask][1]
+		assert.Equal(t, "uid-caldav-test-child-task-2", existingSubTask.UID)
+	})
+
+	//
+	// Edit a subtask and change its parent
+	//
+	t.Run("edit subtask change parent", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		// Edit the subtask:
+		const taskUID = "uid-caldav-test-child-task"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid-caldav-test-child-task
+DTSTAMP:20230301T073337Z
+SUMMARY:Child task for Caldav Test (edited)
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task-2
+END:VTODO
+END:VCALENDAR`
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    task,
+			user:    u,
+		}
+
+		// Edit the task:
+		taskResource, err := storage.UpdateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Check that the result CALDAV contains the new relation:
+		content, _ := taskResource.GetContentData()
+		assert.Contains(t, content, "UID:"+taskUID)
+		assert.Contains(t, content, "RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task-2")
+
+		// Get the task from the DB:
+		tasks, err = models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+
+		// Check that the parent-child relationship has changed to the new parent:
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 1)
+		parentTask := task.RelatedTasks[models.RelationKindParenttask][0]
+		assert.Equal(t, "uid-caldav-test-parent-task-2", parentTask.UID)
+
+		// Get the previous parent from the DB and check that its previous child is gone:
+		tasks, err = models.GetTasksByUIDs(s, []string{"uid-caldav-test-parent-task"}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+		assert.Len(t, task.RelatedTasks[models.RelationKindSubtask], 1)
+		// We're gone, but our former sibling is still there:
+		formerSiblingSubTask := task.RelatedTasks[models.RelationKindSubtask][0]
+		assert.Equal(t, "uid-caldav-test-child-task-2", formerSiblingSubTask.UID)
+	})
+
+	//
+	// Edit a subtask and remove its parent
+	//
+	t.Run("edit subtask remove parent", func(t *testing.T) {
+		db.LoadAndAssertFixtures(t)
+		s := db.NewSession()
+		defer s.Close()
+
+		// Edit the subtask:
+		const taskUID = "uid-caldav-test-child-task"
+		const taskContent = `BEGIN:VCALENDAR
+VERSION:2.0
+METHOD:PUBLISH
+X-PUBLISHED-TTL:PT4H
+X-WR-CALNAME:Project 36 for Caldav tests
+PRODID:-//Vikunja Todo App//EN
+BEGIN:VTODO
+UID:uid-caldav-test-child-task
+DTSTAMP:20230301T073337Z
+SUMMARY:Child task for Caldav Test (edited)
+CREATED:20230301T073337Z
+LAST-MODIFIED:20230301T073337Z
+END:VTODO
+END:VCALENDAR`
+		tasks, err := models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task := tasks[0]
+		storage := &VikunjaCaldavProjectStorage{
+			project: &models.ProjectWithTasksAndBuckets{Project: models.Project{ID: 36}},
+			task:    task,
+			user:    u,
+		}
+
+		// Edit the task:
+		taskResource, err := storage.UpdateResource(taskUID, taskContent)
+		assert.NoError(t, err)
+
+		// Check that the result CALDAV contains the new relation:
+		content, _ := taskResource.GetContentData()
+		assert.Contains(t, content, "UID:"+taskUID)
+		assert.NotContains(t, content, "RELATED-TO;RELTYPE=PARENT:uid-caldav-test-parent-task")
+
+		// Get the task from the DB:
+		tasks, err = models.GetTasksByUIDs(s, []string{taskUID}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+
+		// Check that the parent-child relationship is gone:
+		assert.Len(t, task.RelatedTasks[models.RelationKindParenttask], 0)
+
+		// Get the previous parent from the DB and check that its child is gone:
+		tasks, err = models.GetTasksByUIDs(s, []string{"uid-caldav-test-parent-task"}, u)
+		assert.NoError(t, err)
+		task = tasks[0]
+		// We're gone, but our former sibling is still there:
+		assert.Len(t, task.RelatedTasks[models.RelationKindSubtask], 1)
+		formerSiblingSubTask := task.RelatedTasks[models.RelationKindSubtask][0]
+		assert.Equal(t, "uid-caldav-test-child-task-2", formerSiblingSubTask.UID)
+	})
+}
diff --git a/pkg/routes/caldav/main_test.go b/pkg/routes/caldav/main_test.go
new file mode 100644
index 000000000..7093df18e
--- /dev/null
+++ b/pkg/routes/caldav/main_test.go
@@ -0,0 +1,19 @@
+package caldav
+
+import (
+	"code.vikunja.io/api/pkg/config"
+	"code.vikunja.io/api/pkg/files"
+	"code.vikunja.io/api/pkg/models"
+	"code.vikunja.io/api/pkg/user"
+	"testing"
+)
+
+// TestMain is the main test function used to bootstrap the test env
+func TestMain(m *testing.M) {
+	config.InitDefaultConfig()
+	files.InitTests(true)
+	user.InitTests()
+	models.SetupTests()
+
+	m.Run()
+}