Use JUnit as testing

src/main/java/duke/Parser.java

@@ -20,21 +20,14 @@ public static Command parseCommand(String userInput) throws DukeException {
     }
 
     public static Command addCommand(String command) throws DukeException {
-        String[] cmdLine = command.split(" ");
-        String taskType = cmdLine[0];
-
-        switch (taskType) {
-            case "todo":
-                return new TodoCommand(command);
-
-            case "deadline":
-                return new DeadlineCommand(command);
-
-            case "event":
-                return new EventCommand(command);
-
-            default:
-                throw new DukeException("☹ OOPS!!! I'm sorry, but I don't know what that means :-(");
+        if (command.startsWith("todo")) {
+            return new TodoCommand(command);
+        } else if (command.startsWith("deadline")) {
+            return new DeadlineCommand(command);
+        } else if (command.startsWith("event")) {
+            return new EventCommand(command);
+        } else {
+            throw new DukeException("☹ OOPS!!! I'm sorry, but I don't know what that means :-(");
         }
     }
 }

src/main/java/duke/Storage.java

@@ -1,13 +1,18 @@
 package main.java.duke;
 
 import main.java.duke.exceptions.InvalidFileException;
+import main.java.duke.exceptions.InvalidInputException;
 import main.java.duke.tasks.*;
 
 import java.io.*;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
 
 public class Storage {
 
+    public DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
+
     public final String path;
 
     public Storage(String storagePath) {
@@ -59,10 +64,10 @@ public TaskList load() throws InvalidFileException {
                         newTask = new Todo(readLine[2]);
                         break;
                     case "D":
-                        newTask = new Deadline(readLine[2], readLine[3]);
+                        newTask = new Deadline(readLine[2], LocalDateTime.parse(readLine[3], formatter));
                         break;
                     case "E":
-                        newTask = new Event(readLine[2], readLine[3]);
+                        newTask = new Event(readLine[2], LocalDateTime.parse(readLine[3], formatter));
                         break;
                     default:
                         break;

src/main/java/duke/command/DeadlineCommand.java

@@ -8,24 +8,36 @@
 import main.java.duke.tasks.Task;
 import main.java.duke.tasks.TaskList;
 
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+
 public class DeadlineCommand extends Command {
 
     public static final String MESSAGE_SUCCESS = "Got it. I've added this task:\n";
+    public static final String MESSAGE_PARSE_ERROR = "Invalid date and time format.\n" +
+            "Please enter date and time in the format: yyyy-MM-dd HH:mm";
 
     public DeadlineCommand(String input) {
         super(input);
     }
 
     @Override
     public void execute(TaskList tasks, Ui ui, Storage storage) throws InvalidInputException, InvalidFileException {
-        if (super.input.length() <= 5) {
+        if (super.input.length() <= 8) {
             throw new InvalidInputException("☹ OOPS!!! The description of a deadline cannot be empty.\n");
         }
-        String[] split = super.input.substring(9).split("/by ", 2);
-        Task deadline = new Deadline(split[0], split[1]);
-        tasks.addTask(deadline);
-        ui.printMessage(MESSAGE_SUCCESS + deadline.toString() + "\nNow you have " + tasks.taskListSize() + " tasks in the list.");
-        storage.save(tasks);
+        try {
+            String[] split = super.input.substring(9).split("/by ", 2);
+            DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
+            LocalDateTime date = LocalDateTime.parse(split[1], formatter);
+            Task deadline = new Deadline(split[0], date);
+            tasks.addTask(deadline);
+            ui.printMessage(MESSAGE_SUCCESS + deadline.toString() + "\nNow you have " + tasks.taskListSize() + " tasks in the list.");
+            storage.save(tasks);
+        } catch (DateTimeParseException e) {
+            throw new InvalidInputException(MESSAGE_PARSE_ERROR);
+        }
     }
 
     @Override

src/main/java/duke/command/EventCommand.java

@@ -8,8 +8,15 @@
 import main.java.duke.tasks.Task;
 import main.java.duke.tasks.TaskList;
 
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+import java.time.format.DateTimeParseException;
+import java.util.Date;
+
 public class EventCommand extends Command {
     public static final String MESSAGE_SUCCESS = "Got it. I've added this task:\n";
+    public static final String MESSAGE_PARSE_ERROR = "Invalid date and time format.\n" +
+            "Please enter date and time in the format: yyyy-MM-dd HH:mm";
 
     public EventCommand(String input) {
         super(input);
@@ -20,12 +27,18 @@ public void execute(TaskList tasks, Ui ui, Storage storage) throws InvalidInputE
         if (super.input.length() <= 5) {
             throw new InvalidInputException("☹ OOPS!!! The description of a event cannot be empty.\n");
         }
-        String[] split = super.input.substring(6).split("/at ", 2);
-        Task event = new Event(split[0], split[1]);
-        tasks.addTask(event);
-        ui.printMessage(MESSAGE_SUCCESS + event.toString() + "\nNow you have " + tasks.taskListSize() + " tasks in the list.");
-
-        storage.save(tasks);
+        try {
+            String[] split = super.input.substring(6).split("/at ", 2);
+            DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
+            LocalDateTime date = LocalDateTime.parse(split[1], formatter);
+            Task event = new Event(split[0], date);
+            tasks.addTask(event);
+            ui.printMessage(MESSAGE_SUCCESS + event.toString() + "\nNow you have "
+                    + tasks.taskListSize() + " tasks in the list.");
+            storage.save(tasks);
+        } catch (DateTimeParseException e) {
+            throw new InvalidInputException(MESSAGE_PARSE_ERROR);
+        }
     }
 
     @Override

src/main/java/duke/tasks/Deadline.java

@@ -5,10 +5,9 @@
 public class Deadline extends Task {
     protected LocalDateTime date;
 
-    public Deadline(String description, String date) {
+    public Deadline(String description, LocalDateTime date) {
         super(description);
-        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
-        this.date = LocalDateTime.parse(date, formatter);
+        this.date = date;
     }
 
     @Override

src/main/java/duke/tasks/Event.java

@@ -7,10 +7,9 @@
 public class Event extends Task {
     protected LocalDateTime date;
 
-    public Event(String description, String date) {
+    public Event(String description, LocalDateTime date) {
         super(description);
-        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
-        this.date = LocalDateTime.parse(date, formatter);
+        this.date = date;
     }
 
     @Override

src/test/java/duke/ParserTest.java

@@ -0,0 +1,32 @@
+package test.java.duke;
+
+import main.java.duke.Parser;
+import main.java.duke.command.Command;
+import main.java.duke.exceptions.DukeException;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ParserTest {
+
+    @Test
+    public void testParseCommand() {
+        try {
+            Parser.parseCommand("event read book /at 2020-10-10 20:00");
+            assertTrue(true);
+        } catch (DukeException e) {
+            fail();
+        }
+    }
+
+    @Test
+    public void testParseError() {
+        try {
+            Parser.parseCommand("even read book 2020-10-10 20:00");
+            fail();
+        } catch (DukeException e) {
+            assertTrue(true);
+        }
+    }
+
+}

src/test/java/duke/tasks/DeadlineTest.java

@@ -0,0 +1,28 @@
+package test.java.duke.tasks;
+
+import main.java.duke.tasks.Deadline;
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class DeadlineTest {
+    DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm");
+
+    @Test
+    public void constructorTest() {
+        Deadline deadlineTask = new Deadline("read book ",
+                LocalDateTime.parse("2020-10-10 10:10", formatter));
+        assertEquals("[D][✘] read book (by:10/10/2020 10:10 AM)", deadlineTask.toString());
+    }
+
+    @Test
+    void getState() {
+        Deadline deadlineTask = new Deadline("read book ",
+                LocalDateTime.parse("2020-10-10 10:10", formatter));
+        assertEquals("D|0|read book |2020-10-10 10:10", deadlineTask.getState());
+    }
+
+}

src/test/java/duke/tasks/TodoTest.java

@@ -0,0 +1,29 @@
+package test.java.duke.tasks;
+
+import main.java.duke.tasks.Todo;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+
+class TodoTest {
+
+    @Test
+    public void constructorTest() {
+        Todo todoTask = new Todo("read book");
+        assertEquals("[T][✘] read book", todoTask.toString());
+    }
+
+    @Test
+    void getState() {
+        Todo todoTask = new Todo("read book");
+        assertEquals("T|0|read book", todoTask.getState());
+    }
+
+    @Test
+    void doneTask() {
+        Todo todoTask = new Todo("read book");
+        todoTask.markAsDone();
+        assertEquals("[T][✓] read book", todoTask.toString());
+    }
+}