Add assertions

build.gradle

@@ -54,4 +54,5 @@ shadowJar {
 
 run{
     standardInput = System.in
+    enableAssertions = true
 }

src/main/java/duke/Parser.java

@@ -62,10 +62,11 @@ public String mark(String[] input, TaskList taskList) throws DukeException {
         } catch (NumberFormatException e) {
             throw new DukeException("Invalid number.");
         }
-        if (index > taskList.size()) {
+        if (index > taskList.size() || index <= 0) {
             throw new DukeException("Invalid task.");
         }
-        return taskList.markTask(Integer.parseInt(input[1]) - 1);
+        assert index > 0 : "Number less than equal 0.";
+        return taskList.markTask(index - 1);
     }
 
     /**
@@ -84,10 +85,11 @@ public String unmark(String[] input, TaskList taskList) throws DukeException {
         } catch (NumberFormatException e) {
             throw new DukeException("Invalid number.");
         }
-        if (index > taskList.size()) {
+        if (index > taskList.size() || index <= 0) {
             throw new DukeException("Invalid task.");
         }
-        return taskList.unmarkTask(Integer.parseInt(input[1]) - 1);
+        assert index > 0 : "Number less than equal 0.";
+        return taskList.unmarkTask(index - 1);
     }
 
     /**
@@ -169,9 +171,10 @@ public String delete(String[] input, TaskList taskList) throws DukeException {
         } catch (NumberFormatException e) {
             throw new DukeException("Invalid number.");
         }
-        if (index > taskList.size()) {
+        if (index > taskList.size() || index <= 0) {
             throw new DukeException("Invalid task.");
         }
+        assert index > 0 : "Number less than equal 0.";
         return taskList.deleteTask(index - 1);
     }
 

src/main/java/duke/Storage.java

@@ -38,6 +38,7 @@ public TaskList loadData() throws DukeException {
             if (file.createNewFile()){
                 return taskList;
             }
+            assert file.exists(): "File was not successfully created.";
         } catch (IOException e) {
             throw new DukeException("Something went wrong when accessing file");
         }
@@ -83,7 +84,8 @@ public void storeData(ArrayList<Task> t) throws DukeException {
         try {
             if (file.createNewFile()) {
                 System.out.println("Created new file taskList.txt");
-            } 
+            }
+            assert file.exists(): "File was not successfully created.";
             FileWriter fw = new FileWriter(file);
             String taskString = "";
             for (int i = 0; i < t.size(); i++){

taskList.txt

@@ -1,5 +1,9 @@
-D|0|2|2023-05-05
+D|1|2|2023-05-05
 T|0|3
 T|0|4
 T|0|5
 T|0|6
+D|0||2023-05-25
+E|0|3|2023-12-23|2023-12-24
+E|0|4|2023-12-23|2023-12-24
+E|0|5|2023-03-23|2023-05-06