diff --git a/build.gradle b/build.gradle
index a388517ae1..5c14e041ba 100644
--- a/build.gradle
+++ b/build.gradle
@@ -28,7 +28,7 @@ test {
 }
 
 application {
-    mainClass.set("seedu.duke.Duke")
+    mainClass.set("duke.Duke")
 }
 
 shadowJar {
@@ -37,6 +37,6 @@ shadowJar {
     dependsOn("distZip", "distTar")
 }
 
-run{
+run {
     standardInput = System.in
 }
diff --git a/src/main/java/duke/Parser.java b/src/main/java/duke/Parser.java
index aa89526fe1..29db79a45c 100644
--- a/src/main/java/duke/Parser.java
+++ b/src/main/java/duke/Parser.java
@@ -21,6 +21,7 @@ public class Parser {
      * @return The command to be used by the bot.
      */
     public static Command decideCommand(String input) {
+        // return BYE and LIST only if the input matches exactly
         if (input.equals("bye")) {
             return Command.BYE;
         } else if (input.equals(("list"))) {
@@ -30,7 +31,7 @@ public static Command decideCommand(String input) {
             String command = words[0];
 
             for (Command c : Command.values()) {
-                if (c.name().toLowerCase().equals(command)) {
+                if (c.name().toLowerCase().equals(command) && !c.equals(Command.BYE) && !c.equals(Command.LIST)) {
                     return c;
                 }
             }
diff --git a/src/main/java/duke/TaskList.java b/src/main/java/duke/TaskList.java
index d47af75325..4c3660f639 100644
--- a/src/main/java/duke/TaskList.java
+++ b/src/main/java/duke/TaskList.java
@@ -129,8 +129,8 @@ public void addTodo(String input) throws DukeException {
             addTask(task);
         } else {
             // Todo description is empty
-            throw new DukeException("☹ OOPS!!! The description of a todo cannot be empty."
-                    + "\ntodo ...");
+            throw new DukeException("☹ OOPS!!! The description of a todo cannot be empty." +
+                    "\ntodo ...");
         }
     }
 
@@ -157,8 +157,8 @@ public void addEvent(String input) throws DukeException {
             addTask(task);
         } else {
             // User did not follow event format
-            throw new DukeException("Input for event doesn't match the expected format."
-                    + "\nevent ... /from ... /to ...");
+            throw new DukeException("Input for event doesn't match the expected format." +
+                    "\nevent ... /from ... /to ...");
         }
     }
 
@@ -183,8 +183,8 @@ public void addDeadline(String input) throws DukeException {
             addTask(task);
         } else {
             // User did not follow deadline format
-            throw new DukeException("Input for deadline doesn't match the expected format."
-                    + "\ndeadline ... /by ...");
+            throw new DukeException("Input for deadline doesn't match the expected format." +
+                    "\ndeadline ... /by ...");
         }
     }
 
diff --git a/src/test/java/duke/DeadlineTest.java b/src/test/java/duke/DeadlineTest.java
new file mode 100644
index 0000000000..a9764c61bb
--- /dev/null
+++ b/src/test/java/duke/DeadlineTest.java
@@ -0,0 +1,39 @@
+package duke;
+
+import duke.tasks.Deadline;
+import duke.tasks.Task;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDate;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class DeadlineTest {
+
+    @Test
+    public void testToString() {
+        Task task = new Deadline(LocalDate.of(2023, 6, 23), "abc");
+        assertEquals("[D][ ] abc (by: 2023-06-23)", task.toString());
+    }
+
+    @Test
+    public void testTaskToString() {
+        Task task = new Deadline(LocalDate.of(2023, 6, 23), "abc");
+        assertEquals("D | 0 | abc | 2023-06-23", task.tasktoString());
+    }
+
+    @Test
+    public void testMarkAsDone() {
+        Task task = new Deadline(LocalDate.of(2023, 6, 23), "abc");
+        task.markAsDone();
+        assertEquals("D | 1 | abc | 2023-06-23", task.tasktoString());
+    }
+
+    @Test
+    public void testUnMark() {
+        Task task = new Deadline(LocalDate.of(2023, 6, 23), "abc");
+        task.markAsDone();
+        task.unMark();
+        assertEquals("D | 0 | abc | 2023-06-23", task.tasktoString());
+    }
+}
diff --git a/src/test/java/duke/ParserTest.java b/src/test/java/duke/ParserTest.java
new file mode 100644
index 0000000000..0202c87c8a
--- /dev/null
+++ b/src/test/java/duke/ParserTest.java
@@ -0,0 +1,149 @@
+package duke;
+
+import duke.tasks.Deadline;
+import duke.tasks.Event;
+import duke.tasks.Todo;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDate;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+public class ParserTest {
+    @Test
+    public void decideCommand_invalidInput_invalid() {
+        assertEquals(Command.INVALID, Parser.decideCommand("abc 123"));
+    }
+
+    @Test
+    public void decideCommand_wrongByeFormat_invalid() {
+        assertEquals(Command.INVALID, Parser.decideCommand("bye bye"));
+    }
+
+    @Test
+    public void decideCommand_wrongListInput_invalid() {
+        assertEquals(Command.INVALID, Parser.decideCommand("list 123"));
+    }
+
+    @Test
+    public void decideCommand_eventInput_event() {
+        assertEquals(Command.EVENT, Parser.decideCommand("event abc"));
+    }
+
+    @Test
+    public void decideCommand_deadlineInput_deadline() {
+        assertEquals(Command.DEADLINE, Parser.decideCommand("deadline abc"));
+    }
+
+    @Test
+    public void decideCommand_todoInput_todo() {
+        assertEquals(Command.TODO, Parser.decideCommand("todo abc"));
+    }
+
+    @Test
+    public void decideCommand_markInput_mark() {
+        assertEquals(Command.MARK, Parser.decideCommand("mark abc"));
+    }
+
+    @Test
+    public void decideCommand_unmarkInput_unmark() {
+        assertEquals(Command.UNMARK, Parser.decideCommand("unmark abc"));
+    }
+
+    @Test
+    public void decideCommand_correctListInput_list() {
+        assertEquals(Command.LIST, Parser.decideCommand("list"));
+    }
+
+    @Test
+    public void decideCommand_correctByeInput_bye() {
+        assertEquals(Command.BYE, Parser.decideCommand("bye"));
+    }
+
+    @Test
+    public void stringToTask_incorrectTaskType_exceptionThrown() {
+        try {
+            assertEquals(new Todo("abc").toString(),
+                    Parser.stringToTask("a | 1 | abc").toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Field 1 (Task type) is invalid", e.getMessage());
+        }
+    }
+
+    @Test
+    public void stringToTask_incorrectIsMarked_exceptionThrown() {
+        try {
+            assertEquals(new Todo("abc").toString(), Parser.stringToTask("T | 3 | abc").toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Field 2 (isMarked) is invalid", e.getMessage());
+        }
+    }
+
+    @Test
+    public void stringToTask_incorrectTodoFormat_exceptionThrown() {
+        try {
+            assertEquals(new Todo("abc").toString(), Parser.stringToTask("T | 1").toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Incorrect Format for todo task in file", e.getMessage());
+        }
+    }
+
+    @Test
+    public void stringToTask_incorrectDeadlineFormat_exceptionThrown() {
+        try {
+            assertEquals(new Deadline(LocalDate.of(2023, 6, 23), "abc").toString(),
+                    Parser.stringToTask("D | 0 | abc").toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Incorrect Format for deadline task in file", e.getMessage());
+        }
+    }
+
+    @Test
+    public void stringToTask_incorrectEventFormat_exceptionThrown() {
+        try {
+            assertEquals(new Event(LocalDate.of(2023, 6, 23),
+                            LocalDate.of(2023, 6, 24),
+                            "abc").toString(),
+                    Parser.stringToTask("E | 0 | abc | 2023-06-23").toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Incorrect Format for event task in file", e.getMessage());
+        }
+    }
+
+    @Test
+    public void stringToTask_correctTodoFormat_todoTask() {
+        try {
+            assertEquals(new Todo("abc").toString(),
+                    Parser.stringToTask("T | 0 | abc").toString());
+        } catch (Exception e) {
+            fail();
+        }
+    }
+
+    @Test
+    public void stringToTask_correctDeadlineFormat_deadlineTask() {
+        try {
+            assertEquals(new Deadline(LocalDate.of(2023, 6, 23), "abc").toString(),
+                    Parser.stringToTask("D | 0 | abc | 2023-06-23").toString());
+        } catch (Exception e) {
+            fail();
+        }
+    }
+
+    @Test
+    public void stringToTask_correctEventFormat_eventTask() {
+        try {
+            assertEquals(new Event(LocalDate.of(2023, 6, 23),
+                            LocalDate.of(2023, 6, 24), "abc").toString(),
+                    Parser.stringToTask("E | 0 | abc | 2023-06-23 | 2023-06-24").toString());
+        } catch (Exception e) {
+            fail();
+        }
+    }
+}
diff --git a/src/test/java/duke/TaskListTest.java b/src/test/java/duke/TaskListTest.java
new file mode 100644
index 0000000000..b24d425a68
--- /dev/null
+++ b/src/test/java/duke/TaskListTest.java
@@ -0,0 +1,110 @@
+package duke;
+
+import duke.tasks.Deadline;
+import duke.tasks.Event;
+import duke.tasks.Task;
+import duke.tasks.Todo;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.fail;
+
+public class TaskListTest {
+    List<Task> list = new ArrayList<>();
+    Task task1 = new Todo("abc");
+    Task task2 = new Event(LocalDate.of(2023, 8, 16),
+            LocalDate.of(2023, 8, 27),
+            "read book");
+    Task task3 = new Deadline(LocalDate.of(2023, 5, 23), "read book");
+    private TaskList taskList = new TaskList(list);
+
+    @BeforeEach
+    public void init() {
+        taskList.addTask(task1);
+        taskList.addTask(task2);
+        taskList.addTask(task3);
+    }
+
+    @Test
+    public void addDeadline_wrongInputFormat_exceptionThrown() {
+        try {
+            taskList.addDeadline("deadline read book 2023-04-16");
+            Task task4 = new Deadline(LocalDate.of(2023, 4, 16), "read book");
+            assertEquals(task4.toString(), list.get(3).toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Input for deadline doesn't match the expected format." +
+                    "\ndeadline ... /by ...", e.getMessage());
+        }
+    }
+
+    @Test
+    public void addDeadline_wrongDateFormat_exceptionThrown() {
+        try {
+            taskList.addDeadline("deadline read book 2023-16-04");
+            Task task4 = new Deadline(LocalDate.of(2023, 4, 16), "read book");
+            assertEquals(task4.toString(), list.get(3).toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            assertEquals("Input for deadline doesn't match the expected format." +
+                    "\ndeadline ... /by ...", e.getMessage());
+        }
+    }
+
+    @Test
+    public void addDeadline_correctInput_taskAdded() {
+        try {
+            taskList.addDeadline("deadline read book /by 2023-04-16");
+            Task task4 = new Deadline(LocalDate.of(2023, 4, 16), "read book");
+            assertEquals(task4.toString(), list.get(3).toString());
+        } catch (Exception e) {
+            fail();
+        }
+    }
+
+    @Test
+    public void markTask_invalidNumber_exceptionThrown() {
+        try {
+            Task task4 = new Deadline(LocalDate.of(2023, 5, 23), "read book");
+            task4.markAsDone();
+            taskList.markTask("4");
+            assertEquals(task4.toString(), list.get(2).toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+            assertEquals("Invalid number", e.getMessage());
+        }
+    }
+
+    @Test
+    public void markTask_noNumber_exceptionThrown() {
+        try {
+            Task task4 = new Deadline(LocalDate.of(2023, 5, 23), "read book");
+            task4.markAsDone();
+            taskList.markTask("read book");
+            assertEquals(task4.toString(), list.get(2).toString());
+            fail(); // the test should not reach this line
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+            assertEquals("Please key in a number", e.getMessage());
+        }
+    }
+
+    @Test
+    public void markTask_validNumber_taskMarked() {
+        try {
+            Task task4 = new Deadline(LocalDate.of(2023, 5, 23), "read book");
+            task4.markAsDone();
+            taskList.markTask("3");
+            assertEquals(task4.toString(), list.get(2).toString());
+        } catch (Exception e) {
+            fail();
+        }
+    }
+}