diff --git a/domain-model.md b/domain-model.md
new file mode 100644
index 000000000..7621b35c9
--- /dev/null
+++ b/domain-model.md
@@ -0,0 +1,87 @@
+# Todo list core
+
+## Core Requirements
+
+- I want to add tasks to my todo list.
+- I want to see all the tasks in my todo list.
+- I want to change the status of a task between incomplete and complete.
+- I want to be able to get only the complete tasks.
+- I want to be able to get only the incomplete tasks.
+- I want to search for a task and receive a message that says it wasn't found if it doesn't exist.
+- I want to remove tasks from my list.
+- I want to see all the tasks in my list ordered alphabetically in ascending order.
+- I want to see all the tasks in my list ordered alphabetically in descending order.
+
+
+## TodoList Class
+
+
+
+| Member variable | Data type         |
+|-----------------|-------------------|
+| `task`          | `Task`            |
+| `todoList`      | `ArrayList<task>` |
+|                 |                   |
+
+#### Task Class
+| Member variable | Data type |
+|-----------------|-----------|
+| `taskName`      | `String`  |
+| `taskStatus`    | `String`  |
+
+
+
+
+| Method                   | Scenario                                                                            | Output                                                                                    |
+|--------------------------|-------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------|
+| `addTask(String)`        | Task is added to todoList<br/>Task is not added to todoList                         | `Return` true<br/>`Return` false                                                          |
+| `getTasks()`             | todoList is not empty<br/>todoList is empty                                         | `Return` all tasks in todo list<br/>`Return` "Todo list is empty."                        |
+| `getCompletedTasks()`    | todoList contains completed tasks<br/>todoList does not contain completed tasks     | `Return` tasks with status 'complete'<br/>`Return` "No completed tasks in todo list."     |
+| `getUncompletedTasks()`  | todoList contains uncompleted tasks<br/>todoList does not contain uncompleted tasks | `Return` tasks with status 'incomplete'<br/>`Return` "No uncompleted tasks in todo list." |
+| `searchTask(String)`     | Task exists in todoList<br/>Task does not exist in todoList                         | `Return` task<br/>`Return` "Task not found."                                              |
+| `setCompleted(String)`   | Task exists in todoList<br/>Task does not exist in todoList                         | `Return` "Task status is now 'Completed'."<br/>`Return` "Task not found."                 |
+| `setUncompleted(String)` | Task exists in todoList<br/>Task does not exist in todoList                         | `Return` "Task status is now 'Incomplete'."<br/>`Return` "Task not found."                |                                                                                                                
+| `removeTask(String)`     | Task exist in todoList<br/>Task does not exist in todoList                          | `Return` "Task removed from todo list."<br/>`Return` "Task not found."                    |
+| `getTasksAscending()`    | todoList is not empty<br/>todoList is empty                                         | `Return` all tasks in todo list in ascending order<br/>`Return` "Todo list is empty."     |
+| `getTasksDescending()`   | todoList is not empty<br/>todoList is empty                                         | `Return` all tasks in todo list in descending order<br/>`Return` "Todo list is empty."    |
+
+
+# Todo list extension
+
+| Member variable | Data type         |
+|-----------------|-------------------|
+| `task`          | `Task`            |
+| `todoList`      | `ArrayList<task>` |
+| `idCounter`     | `int`             |
+
+#### Task Class
+| Member variable | Data type       |
+|-----------------|-----------------|
+| `taskId`        | `int`           |
+| `taskName`      | `String`        |
+| `taskStatus`    | `String`        |
+| `dateTime`      | `LocalDateTime` |
+
+
+
+
+| Method                      | Scenario                                                                            | Output                                                                                                          |
+|-----------------------------|-------------------------------------------------------------------------------------|-----------------------------------------------------------------------------------------------------------------|
+| `addTask(String)`           | Task is added to todoList<br/>Task is not added to todoList                         | `Return` true<br/>`Return` false                                                                                |
+| `getTasks()`                | todoList is not empty<br/>todoList is empty                                         | `Return` all tasks in todo list<br/>`Return` "Todo list is empty."                                              |
+| `getCompletedTasks()`       | todoList contains completed tasks<br/>todoList does not contain completed tasks     | `Return` tasks with status 'complete'<br/>`Return` "No completed tasks in todo list."                           |
+| `getUncompletedTasks()`     | todoList contains uncompleted tasks<br/>todoList does not contain uncompleted tasks | `Return` tasks with status 'incomplete'<br/>`Return` "No uncompleted tasks in todo list."                       |
+| `searchTask(String)`        | Task exists in todoList<br/>Task does not exist in todoList                         | `Return` task<br/>`Return` "Task not found."                                                                    |
+| `setCompleted(String)`      | Task exists in todoList<br/>Task does not exist in todoList                         | `Return` "Task status is now 'Completed'."<br/>`Return` "Task not found."                                       |
+| `setUncompleted(String)`    | Task exists in todoList<br/>Task does not exist in todoList                         | `Return` "Task status is now 'Incomplete'."<br/>`Return` "Task not found."                                      |
+| `removeTask(String)`        | Task exist in todoList<br/>Task does not exist in todoList                          | `Return` "Task removed from todo list."<br/>`Return` "Task not found."                                          |
+| `getTasksAscending()`       | todoList is not empty<br/>todoList is empty                                         | `Return` all tasks in todo list in ascending order<br/>`Return` "Todo list is empty."                           |
+| `getTasksDescending()`      | todoList is not empty<br/>todoList is empty                                         | `Return` all tasks in todo list in descending order<br/>`Return` "Todo list is empty."                          |
+| `getTaskById(int)`          | Task exists in todoList<br/>Task does not exist in todoList<br/>todoList is empty   | `Return` task<br/>`Return` "Task not found."<br/>`Return` "Todo list is empty."                                 |
+| `editTaskName(int, String)` | Task exists in todoList<br/>Task does not exist in todoList<br/>todoList is empty   | `Return` "Task name changed."<br/>`Return` "Task not found." <br/>`Return` "Todo list is empty."                |
+| `setCompletedById(int)`     | Task exists in todoList<br/>Task does not exist in todoList<br/>todoList is empty   | `Return` "Task status is now 'Completed'."<br/>`Return` "Task not found." <br/>`Return` "Todo list is empty."   |
+| `setUncompletedById(int)`   | Task exists in todoList<br/>Task does not exist in todoList<br/>todoList is empty   | `Return` "Task status is now 'Incomplete'."<br/>`Return` "Task not found."  <br/>`Return` "Todo list is empty." |                                                                                                                                              
+| `getCreationDateTime(int)`  | Task exists in todoList<br/>Task does not exist in todoList<br/>todoList is empty   | `Return` "Task was created at 'DateTime'"<br/>`Return` "Task not found."  <br/>`Return` "Todo list is empty."   |
+
+
+
diff --git a/src/main/java/com/booleanuk/core/TodoList.java b/src/main/java/com/booleanuk/core/TodoList.java
index 675adaf0b..6e5bdd120 100644
--- a/src/main/java/com/booleanuk/core/TodoList.java
+++ b/src/main/java/com/booleanuk/core/TodoList.java
@@ -1,5 +1,136 @@
 package com.booleanuk.core;
 
+import java.util.*;
+
 public class TodoList {
 
+    public static class Task{
+        public String taskName;
+        public String taskStatus;
+    }
+
+    ArrayList<Task> todoList = new ArrayList<>();
+
+    public Boolean addTask(String taskName){
+        Task task = new Task();
+        task.taskName=taskName;
+        task.taskStatus="Incomplete";
+        this.todoList.add(task);
+        return true;
+    }
+
+    public String getTasks(){
+        if (!this.todoList.isEmpty()){
+            ArrayList<String> taskNames = new ArrayList<>();
+            for (Task task : todoList) {
+                taskNames.add(task.taskName);
+            }
+            return taskNames.toString();
+        }else {
+            return "Todo list is empty.";
+        }
+    }
+
+    public String setCompleted(String taskName){
+        Task task = new Task();
+        task.taskStatus = "Completed";
+        task.taskName = taskName;
+
+        for (int i=0;i<todoList.size();i++){
+            if (taskName.equals((todoList.get(i)).taskName)){
+                todoList.set(i, task);
+                return "Task status is now 'Completed'.";
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String setUncompleted(String taskName){
+        Task task = new Task();
+        task.taskStatus = "Incomplete";
+        task.taskName = taskName;
+
+        for (int i=0;i<todoList.size();i++){
+            if (taskName.equals((todoList.get(i)).taskName)){
+                todoList.set(i, task);
+                return "Task status is now 'Incomplete'.";
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String getCompletedTasks(){
+        ArrayList<String> completedTasks = new ArrayList<>();
+        for (Task task : todoList) {
+            if (task.taskStatus.equals("Completed")) {
+                completedTasks.add(task.taskName);
+            }
+        }
+        if (!completedTasks.isEmpty()){
+            return completedTasks.toString();
+        }else {
+            return "No completed tasks in todo list.";
+        }
+    }
+
+    public String getUncompletedTasks(){
+        ArrayList<String> uncompletedTasks = new ArrayList<>();
+        for (Task task : todoList) {
+            if (task.taskStatus.equals("Incomplete")) {
+                uncompletedTasks.add(task.taskName);
+            }
+        }
+        if (!uncompletedTasks.isEmpty()){
+            return uncompletedTasks.toString();
+        }else {
+            return "No uncompleted tasks in todo list.";
+        }
+    }
+
+    public String searchTask(String taskName){
+        for (Task task : todoList) {
+            if (taskName.equals(task.taskName)) {
+                return "Task '" + taskName + "' is " + task.taskStatus;
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String removeTask(String taskName) {
+        for (int i = 0; i < todoList.size(); i++) {
+            if (taskName.equals((todoList.get(i)).taskName)) {
+                todoList.remove(i);
+                return "Task removed from todo list.";
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String getTasksAscending(){
+        if (!this.todoList.isEmpty()){
+            ArrayList<String> taskNames = new ArrayList<>();
+            for (Task task : todoList) {
+                taskNames.add(task.taskName);
+            }
+            Collections.sort(taskNames);
+            return taskNames.toString();
+        }else {
+            return "Todo list is empty.";
+        }
+    }
+
+    public String getTasksDescending(){
+        Comparator<String> reverseComparator = Comparator.reverseOrder();
+        if (!this.todoList.isEmpty()){
+            ArrayList<String> taskNames = new ArrayList<>();
+            for (Task task : todoList) {
+                taskNames.add(task.taskName);
+            }
+            taskNames.sort(reverseComparator);
+            return taskNames.toString();
+        }else {
+            return "Todo list is empty.";
+        }
+    }
+
 }
diff --git a/src/main/java/com/booleanuk/extension/TodoListExtension.java b/src/main/java/com/booleanuk/extension/TodoListExtension.java
new file mode 100644
index 000000000..d7394b203
--- /dev/null
+++ b/src/main/java/com/booleanuk/extension/TodoListExtension.java
@@ -0,0 +1,240 @@
+package com.booleanuk.extension;
+
+import com.booleanuk.core.TodoList;
+
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
+
+public class TodoListExtension {
+
+    public static class Task{
+        public int taskId;
+        public String taskName;
+        public String taskStatus;
+        public LocalDateTime dateTime;
+    }
+
+    ArrayList<Task> todoList = new ArrayList<>();
+    int idCounter = 1;
+
+    // Extension methods
+
+    public String getTaskById(int taskId){
+        if (!todoList.isEmpty()){
+            for (Task task : todoList) {
+                if (taskId == task.taskId) {
+                    return "'" + task.taskName + "' is " + task.taskStatus;
+                }
+            }
+            return "Task not found.";
+        }
+        else {
+            return "Todo list is empty.";
+        }
+    }
+
+    public String editTaskName(int taskId, String newTaskName){
+        if (!todoList.isEmpty()){
+            for (int i=0;i<todoList.size();i++) {
+                if (taskId == todoList.get(i).taskId) {
+                    // Create new task object with updated name for insertion into list
+                    Task editedTask = new Task();
+                    editedTask.taskId=taskId;
+                    editedTask.taskName=newTaskName;
+                    editedTask.taskStatus=todoList.get(i).taskStatus;
+                    editedTask.dateTime=todoList.get(i).dateTime;
+                    todoList.set(i, editedTask);
+                    return "Task name changed to '" + todoList.get(i).taskName + "'";
+                }
+            }
+            return "Task not found.";
+        }
+        else {
+            return "Todo list is empty.";
+        }
+    }
+
+    public String setCompletedById(int taskId){
+        if (!todoList.isEmpty()){
+            for (int i=0;i<todoList.size();i++){
+                if (taskId == todoList.get(i).taskId){
+                    // Create new task object with updated status for insertion into list
+                    Task editedTask = new Task();
+                    editedTask.taskId=taskId;
+                    editedTask.taskName=todoList.get(i).taskName;
+                    editedTask.taskStatus="Completed";
+                    editedTask.dateTime=todoList.get(i).dateTime;
+                    todoList.set(i, editedTask);
+                    return "Task status is now 'Completed'.";
+                }
+            }
+            return "Task not found.";
+        }else {
+            return "Task list is empty.";
+        }
+    }
+
+    public String setUncompletedById(int taskId){
+        if (!todoList.isEmpty()){
+            for (int i=0;i<todoList.size();i++){
+                if (taskId == todoList.get(i).taskId){
+                    // Create new task object with updated status for insertion into list
+                    Task editedTask = new Task();
+                    editedTask.taskId=taskId;
+                    editedTask.taskName=todoList.get(i).taskName;
+                    editedTask.taskStatus="Incomplete";
+                    editedTask.dateTime=todoList.get(i).dateTime;
+                    todoList.set(i, editedTask);
+                    return "Task status is now 'Incomplete'.";
+                }
+            }
+            return "Task not found.";
+        }else {
+            return "Task list is empty.";
+        }
+    }
+
+    public String getCreationDateTime(int taskId){
+        if (!todoList.isEmpty()){
+            for (Task task : todoList) {
+                if (taskId == task.taskId) {
+                    return "Task created at '" + task.dateTime.toString() + "' is " + task.taskStatus;
+                }
+            }
+            return "Task not found.";
+        }
+        else {
+            return "Todo list is empty.";
+        }
+    }
+
+
+    // Core methods
+
+    public Boolean addTask(String taskName){
+        Task task = new Task();
+        task.taskId= idCounter;
+        task.taskName=taskName;
+        task.taskStatus="Incomplete";
+        task.dateTime=LocalDateTime.now().withNano(0).withSecond(0);
+        this.todoList.add(task);
+        idCounter++;
+        return true;
+    }
+
+    public String getTasks(){
+        if (!this.todoList.isEmpty()){
+            ArrayList<String> taskNames = new ArrayList<>();
+            for (Task task : todoList) {
+                taskNames.add(task.taskName);
+            }
+            return taskNames.toString();
+        }else {
+            return "Todo list is empty.";
+        }
+    }
+
+    public String setCompleted(String taskName){
+        Task task = new Task();
+        task.taskStatus = "Completed";
+        task.taskName = taskName;
+
+        for (int i=0;i<todoList.size();i++){
+            if (taskName.equals((todoList.get(i)).taskName)){
+                todoList.set(i, task);
+                return "Task status is now 'Completed'.";
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String setUncompleted(String taskName){
+        Task task = new Task();
+        task.taskStatus = "Incomplete";
+        task.taskName = taskName;
+
+        for (int i=0;i<todoList.size();i++){
+            if (taskName.equals((todoList.get(i)).taskName)){
+                todoList.set(i, task);
+                return "Task status is now 'Incomplete'.";
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String getCompletedTasks(){
+        ArrayList<String> completedTasks = new ArrayList<>();
+        for (Task task : todoList) {
+            if (task.taskStatus.equals("Completed")) {
+                completedTasks.add(task.taskName);
+            }
+        }
+        if (!completedTasks.isEmpty()){
+            return completedTasks.toString();
+        }else {
+            return "No completed tasks in todo list.";
+        }
+    }
+
+    public String getUncompletedTasks(){
+        ArrayList<String> uncompletedTasks = new ArrayList<>();
+        for (Task task : todoList) {
+            if (task.taskStatus.equals("Incomplete")) {
+                uncompletedTasks.add(task.taskName);
+            }
+        }
+        if (!uncompletedTasks.isEmpty()){
+            return uncompletedTasks.toString();
+        }else {
+            return "No uncompleted tasks in todo list.";
+        }
+    }
+
+    public String searchTask(String taskName){
+        for (Task task : todoList) {
+            if (taskName.equals(task.taskName)) {
+                return "Task '" + taskName + "' is " + task.taskStatus;
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String removeTask(String taskName) {
+        for (int i = 0; i < todoList.size(); i++) {
+            if (taskName.equals((todoList.get(i)).taskName)) {
+                todoList.remove(i);
+                return "Task removed from todo list.";
+            }
+        }
+        return "Task not found.";
+    }
+
+    public String getTasksAscending(){
+        if (!this.todoList.isEmpty()){
+            ArrayList<String> taskNames = new ArrayList<>();
+            for (Task task : todoList) {
+                taskNames.add(task.taskName);
+            }
+            Collections.sort(taskNames);
+            return taskNames.toString();
+        }else {
+            return "Todo list is empty.";
+        }
+    }
+
+    public String getTasksDescending(){
+        Comparator<String> reverseComparator = Comparator.reverseOrder();
+        if (!this.todoList.isEmpty()){
+            ArrayList<String> taskNames = new ArrayList<>();
+            for (Task task : todoList) {
+                taskNames.add(task.taskName);
+            }
+            taskNames.sort(reverseComparator);
+            return taskNames.toString();
+        }else {
+            return "Todo list is empty.";
+        }
+    }
+}
diff --git a/src/test/java/com/booleanuk/core/TodoListTest.java b/src/test/java/com/booleanuk/core/TodoListTest.java
index 0bef779a4..509ffbcb9 100644
--- a/src/test/java/com/booleanuk/core/TodoListTest.java
+++ b/src/test/java/com/booleanuk/core/TodoListTest.java
@@ -3,11 +3,148 @@
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
+import java.util.ArrayList;
+
 class TodoListTest {
     @Test
-    public void exampleTest() {
-        String hello = "Hello";
-        Assertions.assertEquals("Hello", hello);
-        Assertions.assertNotEquals("Goodbye", hello);
+    public void testAddTask() {
+        TodoList todoList = new TodoList();
+
+        // Test that task is added to list
+        Assertions.assertTrue(todoList.addTask("Test task 1"));
+        Assertions.assertEquals("[Test task 1]", todoList.getTasks());
+    }
+
+    @Test
+    public void testGetTasks(){
+        TodoList todoList = new TodoList();
+
+        // Test if return is correct when list is empty
+        Assertions.assertEquals("Todo list is empty.", todoList.getTasks());
+
+        // Test if tasks are retrieved
+        todoList.addTask("Test task 1");
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        ArrayList<String> test = new ArrayList<>();
+        test.add("Test task 1");
+        test.add("Test task 2");
+        test.add("Test task 3");
+        Assertions.assertEquals(test.toString(), todoList.getTasks());
+    }
+
+    @Test
+    public void testChangeStatus() {
+        TodoList todoList = new TodoList();
+
+        // Test if return is correct when task does not exist
+        Assertions.assertEquals("Task not found.", todoList.setCompleted("Test task 1"));
+
+        // Test that the status is changed to complete
+        todoList.addTask("Test task 1");
+        Assertions.assertEquals("Task status is now 'Completed'.", todoList.setCompleted("Test task 1"));
+
+        // Test that the status is changed to incomplete
+        Assertions.assertEquals("Task status is now 'Incomplete'.", todoList.setUncompleted("Test task 1"));
+
+    }
+
+    @Test
+    public void testGetCompletedTasks() {
+        TodoList todoList = new TodoList();
+
+        // Test that no tasks are retrieved if no tasks have status complete
+        todoList.addTask("Test task 1");
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("No completed tasks in todo list.", todoList.getCompletedTasks());
+
+        // Test that tasks with status complete are retrieved
+        todoList.setCompleted("Test task 1");
+        todoList.setCompleted("Test task 3");
+        Assertions.assertEquals("[Test task 1, Test task 3]", todoList.getCompletedTasks());
+    }
+
+    @Test
+    public void testGetUncompletedTasks() {
+        TodoList todoList = new TodoList();
+
+        // Test that no tasks are retrieved if no tasks have status incomplete
+        todoList.addTask("Test task 1");
+        todoList.setCompleted("Test task 1");
+        Assertions.assertEquals("No uncompleted tasks in todo list.", todoList.getUncompletedTasks());
+
+        // Test that tasks with status incomplete are retrieved
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        ArrayList<String> test = new ArrayList<>();
+        test.add("Test task 2");
+        test.add("Test task 3");
+        Assertions.assertEquals(test.toString(), todoList.getUncompletedTasks());
+    }
+
+    @Test
+    public void testSearchTask() {
+        TodoList todoList = new TodoList();
+
+        // Test if return is correct when task does not exist
+        Assertions.assertEquals("Task not found.", todoList.searchTask("Test task 1"));
+
+        // Test if correct task is retrieved by task name
+        todoList.addTask("Test task 1");
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("Task 'Test task 1' is Incomplete", todoList.searchTask("Test task 1"));
+    }
+
+    @Test
+    public void testRemoveTask() {
+        TodoList todoList = new TodoList();
+
+        // Test if return is correct when task does not exist
+        Assertions.assertEquals("Task not found.", todoList.removeTask("Test task 1"));
+
+        // Test if task is removed from list
+        todoList.addTask("Test task 1");
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("Task removed from todo list.", todoList.removeTask("Test task 1"));
+        Assertions.assertEquals("[Test task 2, Test task 3]", todoList.getTasks());
+    }
+
+    @Test
+    public void testGetTasksAscending() {
+        TodoList todoList = new TodoList();
+
+        // Test if return is correct when list is empty
+        Assertions.assertEquals("Todo list is empty.", todoList.getTasksAscending());
+
+        // Test if tasks are retrieved in ascending order
+        todoList.addTask("C task 1");
+        todoList.addTask("A task 2");
+        todoList.addTask("F task 3");
+        ArrayList<String> test = new ArrayList<>();
+        test.add("A task 2");
+        test.add("C task 1");
+        test.add("F task 3");
+        Assertions.assertEquals(test.toString(), todoList.getTasksAscending());
+    }
+
+    @Test
+    public void testGetTasksDescending() {
+        TodoList todoList = new TodoList();
+
+        // Test if return is correct when list is empty
+        Assertions.assertEquals("Todo list is empty.", todoList.getTasksDescending());
+
+        // Test if tasks are retrieved in descending order
+        todoList.addTask("C task 1");
+        todoList.addTask("A task 2");
+        todoList.addTask("F task 3");
+        ArrayList<String> test = new ArrayList<>();
+        test.add("F task 3");
+        test.add("C task 1");
+        test.add("A task 2");
+        Assertions.assertEquals(test.toString(), todoList.getTasksDescending());
     }
 }
diff --git a/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java b/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java
new file mode 100644
index 000000000..09a2bcbc6
--- /dev/null
+++ b/src/test/java/com/booleanuk/extension/TodoListExtensionTest.java
@@ -0,0 +1,71 @@
+package com.booleanuk.extension;
+
+import com.booleanuk.core.TodoList;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDateTime;
+
+public class TodoListExtensionTest {
+    @Test
+    public void testGetTaskById() {
+        TodoListExtension todoList = new TodoListExtension();
+
+        // Test if return is correct when list is empty
+        Assertions.assertEquals("Todo list is empty.", todoList.getTaskById(2));
+
+        // Test if return is correct when task does not exist
+        todoList.addTask("Test task 1");
+        Assertions.assertEquals("Task not found.", todoList.getTaskById(2));
+
+        // Test if correct task is retrieved by id
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("'Test task 2' is Incomplete", todoList.getTaskById(2));
+    }
+    @Test
+    public void testEditTaskName() {
+        TodoListExtension todoList = new TodoListExtension();
+
+        // Test if name is updated by providing id and new name
+        todoList.addTask("Test task 1");
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("Task name changed to 'Edited name'", todoList.editTaskName(2, "Edited name"));
+
+        // Double check that the new name is set correct in the task object
+        Assertions.assertEquals("'Edited name' is Incomplete", todoList.getTaskById(2));
+    }
+
+    @Test
+    public void testChangeStatus() {
+        TodoListExtension todoList = new TodoListExtension();
+
+        // Test if return is correct when list is empty
+        Assertions.assertEquals("Task list is empty.", todoList.setCompletedById(2));
+
+        // Test if return is correct when task does not exist
+        todoList.addTask("Test task 1");
+        Assertions.assertEquals("Task not found.", todoList.setCompletedById(2));
+
+        // Test that the status is changed to complete
+        todoList.addTask("Test task 2");
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("Task status is now 'Completed'.", todoList.setCompletedById(2));
+
+        // Test that the status is changed to incomplete
+        Assertions.assertEquals("Task status is now 'Incomplete'.", todoList.setUncompletedById(2));
+    }
+
+    @Test
+    public void testGetCreationDateTime() {
+        TodoListExtension todoList = new TodoListExtension();
+
+        // Test that the creation datetime is retrieved
+        todoList.addTask("Test task 1");
+        todoList.addTask("Test task 2");
+        String timeNow = LocalDateTime.now().withNano(0).withSecond(0).toString();
+        todoList.addTask("Test task 3");
+        Assertions.assertEquals("Task created at '" + timeNow + "' is Incomplete", todoList.getCreationDateTime(2));
+    }
+}