diff --git a/src/main/java/commands/AddCommand.java b/src/main/java/commands/AddCommand.java
index f76d963375..d6964db058 100644
--- a/src/main/java/commands/AddCommand.java
+++ b/src/main/java/commands/AddCommand.java
@@ -35,7 +35,7 @@ public boolean isExit() {
         return false;
     }
 
-    public String addToDo(TaskList tasks, String input) throws WeiException {
+    private String addToDo(TaskList tasks, String input) throws WeiException {
         if (input.length() < 5) {
             throw new WeiException("please tell me what is your task about");
         }
@@ -43,7 +43,7 @@ public String addToDo(TaskList tasks, String input) throws WeiException {
         return tasks.add(todo);
     }
 
-    public String addDeadline(TaskList tasks, String input) throws WeiException {
+    private String addDeadline(TaskList tasks, String input) throws WeiException {
         try {
             int index = input.indexOf("/");
             String task = input.substring(9, index - 1);
@@ -56,7 +56,7 @@ public String addDeadline(TaskList tasks, String input) throws WeiException {
         }
     }
 
-    public String addEvent(TaskList tasks, String input) throws WeiException {
+    private String addEvent(TaskList tasks, String input) throws WeiException {
         try {
             int firstIndex = input.indexOf("/");
             int secondIndex = input.lastIndexOf("/");
diff --git a/src/main/java/tasks/Deadline.java b/src/main/java/tasks/Deadline.java
index 477a0b0c5b..596a541394 100644
--- a/src/main/java/tasks/Deadline.java
+++ b/src/main/java/tasks/Deadline.java
@@ -18,7 +18,7 @@ public Deadline(String task, String date, boolean status) {
     @Override
     public String stringify() {
         String formattedDate = this.date.format(DateTimeFormatter.ofPattern("MMM d yyyy"));
-        return "[D]" + super.stringify() + "(by: " + formattedDate + ")";
+        return "[D]" + super.stringify() + " (by: " + formattedDate + ")";
     }
 
     @Override
diff --git a/src/main/java/ui/Ui.java b/src/main/java/ui/Ui.java
index 48051d8b00..55a9a32742 100644
--- a/src/main/java/ui/Ui.java
+++ b/src/main/java/ui/Ui.java
@@ -2,7 +2,7 @@
 
 public class Ui {
     public void showLine() {
-        System.out.println("______________________________");
+        System.out.println("________________________________________");
     }
 
     public void greet() {
diff --git a/src/test/java/tasks/DeadlineTest.java b/src/test/java/tasks/DeadlineTest.java
new file mode 100644
index 0000000000..ed6d39e7d6
--- /dev/null
+++ b/src/test/java/tasks/DeadlineTest.java
@@ -0,0 +1,25 @@
+package tasks;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class DeadlineTest {
+    @Test
+    public void testStringify_(){
+        Deadline deadline = new Deadline("read book", "2024-02-03");
+        assertEquals("[D][ ] read book (by: Feb 3 2024)", deadline.stringify());
+
+        Deadline markedDeadline = new Deadline("play", "2024-02-03", true);
+        assertEquals("[D][X] play (by: Feb 3 2024)", markedDeadline.stringify());
+    }
+
+    @Test
+    public void testToString(){
+        Deadline deadline = new Deadline("read book", "2024-02-03");
+        assertEquals("D | O | read book | 2024-02-03", deadline.toString());
+
+        Deadline markedDeadline = new Deadline("play", "2024-02-03", true);
+        assertEquals("D | X | play | 2024-02-03", markedDeadline.toString());
+    }
+}
diff --git a/src/test/java/tasks/TodoTest.java b/src/test/java/tasks/TodoTest.java
new file mode 100644
index 0000000000..9f6b4905dd
--- /dev/null
+++ b/src/test/java/tasks/TodoTest.java
@@ -0,0 +1,25 @@
+package tasks;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class TodoTest {
+    @Test
+    public void testStringify_(){
+        ToDo todo = new ToDo("read book");
+        assertEquals("[T][ ] read book", todo.stringify());
+
+        ToDo markedTodo = new ToDo("play", true);
+        assertEquals("[T][X] play", markedTodo.stringify());
+    }
+
+    @Test
+    public void testToString(){
+        ToDo todo = new ToDo("read book");
+        assertEquals("T | O | read book", todo.toString());
+
+        ToDo markedTodo = new ToDo("play", true);
+        assertEquals("T | X | play", markedTodo.toString());
+    }
+}