Make basic JUnit tests

src/main/java/duke/Duke.java

@@ -12,20 +12,21 @@ public static void main(String[] args) {
 
         Storage.loadTasksFromFile(taskList);
 
-        Ui.printIntroMsg();
+        Ui ui = new Ui();
+        ui.printIntroMsg();
 
         input = scanner.nextLine();
 
         while (!input.equals("bye")) {
-            Ui.printSeparator();
+            ui.printSeparator();
             Parser.parse(input, taskList);
             Storage.updateTasksFile(taskList);
-            Ui.printSeparator();
+            ui.printSeparator();
             input = scanner.nextLine();
         }
 
         scanner.close();
-        Ui.printOutroMsg();
+        ui.printOutroMsg();
     }
 
 }

src/main/java/duke/TaskList.java

@@ -28,10 +28,17 @@ public static void markTask(String[] inputParts, ArrayList<Task> taskList, boole
     }
 
     public static void deleteTask(String[] inputParts, ArrayList<Task> taskList) {
-        int index = Integer.parseInt(inputParts[1]) - 1;
-        Task removedTask = taskList.remove(index);
-        System.out.println("Noted. I've removed this task:\n" + removedTask);
-        System.out.println("Now you have " + taskList.size() + " tasks in the list.");
+        try {
+            int index = Integer.parseInt(inputParts[1]) - 1;
+            if (index > taskList.size()) {
+                throw new DukeException("☹ OOPS!!! Unable to delete non-existent task");
+            }
+            Task removedTask = taskList.remove(index);
+            System.out.println("Noted. I've removed this task:\n" + removedTask);
+            System.out.println("Now you have " + taskList.size() + " tasks in the list.");
+        } catch (DukeException e) {
+            System.out.println(e);
+        }
     }
 
     public static void addTask(String[] inputParts, ArrayList<Task> taskList) {

src/main/java/duke/Ui.java

@@ -11,15 +11,15 @@ public class Ui {
             + "Bye. Hope to see you again soon!\n"
             + LINE_SEPARATOR;
 
-    public static void printIntroMsg() {
+    public void printIntroMsg() {
         System.out.println(GREETING_MESSAGE);
     }
 
-    public static void printOutroMsg() {
+    public void printOutroMsg() {
         System.out.println(GOODBYE_MESSAGE);
     }
 
-    public static void printSeparator() {
+    public void printSeparator() {
         System.out.println(LINE_SEPARATOR);
     }
 

src/test/java/duke/DeadlineTest.java

@@ -0,0 +1,13 @@
+package duke;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class DeadlineTest {
+    @Test
+    public void deadlineTest() {
+        Deadline dl = new Deadline("test", "2019-10-15");
+        assertEquals("Oct 15 2019", dl.getBy());
+    }
+}

src/test/java/duke/EventTest.java

@@ -0,0 +1,13 @@
+package duke;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class EventTest {
+    @Test
+    public void eventTest() {
+        Event dl = new Event("test", "2019-10-15", "2019-10-16");
+        assertEquals("Oct 15 2019 to Oct 16 2019", dl.getFromTo());
+    }
+}