Add tests

src/main/java/seedu/address/logic/commands/RedoCommand.java

@@ -16,7 +16,7 @@ public class RedoCommand extends Command {
     public static final String MESSAGE_USAGE = COMMAND_WORD
             + ": Redo the most recent command that was undone.";
 
-    private static final String MESSAGE_SUCCESS =
+    public static final String MESSAGE_SUCCESS =
             "The last command that modified the employee list has been redone!\n"
             + "Successfully redone the following command: %1$s";
 

src/main/java/seedu/address/logic/commands/UndoCommand.java

@@ -16,7 +16,7 @@ public class UndoCommand extends Command {
     public static final String MESSAGE_USAGE = COMMAND_WORD
             + ": Undo the most recent command that modified the employee list.";
 
-    private static final String MESSAGE_SUCCESS =
+    public static final String MESSAGE_SUCCESS =
             "The last command that modified the employee list has been undone!\n"
             + "Successfully undone the following command: %1$s";
 

src/main/java/seedu/address/model/AddressBookList.java

@@ -8,9 +8,9 @@
  * Represents the history of AddressBook to allow undo and redo.
  */
 public class AddressBookList extends ArrayList<AddressBook> {
-    private static final String REDO_ERROR_MESSAGE = "There is no command to redo! "
+    public static final String REDO_ERROR_MESSAGE = "There is no command to redo! "
             + "The command to be redone need to previously modified the employee list.";
-    private static final String UNDO_ERROR_MESSAGE = "There is no command to undo! "
+    public static final String UNDO_ERROR_MESSAGE = "There is no command to undo! "
             + "The command to be undone need to previously modified the employee list.";
 
     private ArrayList<String> pastCommands = new ArrayList<String>();

src/test/java/seedu/address/logic/commands/RedoCommandTest.java

@@ -0,0 +1,32 @@
+package seedu.address.logic.commands;
+
+import org.junit.jupiter.api.Test;
+
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandSuccess;
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandFailure;
+import static seedu.address.testutil.TypicalPersons.ALICE;
+import static seedu.address.testutil.TypicalPersons.BENSON;
+
+import seedu.address.model.AddressBookList;
+import seedu.address.model.Model;
+import seedu.address.model.ModelManager;
+
+public class RedoCommandTest {
+    private Model model = new ModelManager();
+    private RedoCommand command = new RedoCommand();
+
+    @Test
+    public void execute_redo_success() {
+        model.addPerson(ALICE);
+        model.addCommandText("add Alice");
+        model.addPerson(BENSON);
+        model.addCommandText("add Benson");
+        model.undo();
+        assertCommandSuccess(command, model, String.format(RedoCommand.MESSAGE_SUCCESS, "add Benson"), model);
+    }
+
+    @Test
+    public void execute_redo_failure() {
+        assertCommandFailure(command, model, AddressBookList.REDO_ERROR_MESSAGE);
+    }
+}

src/test/java/seedu/address/logic/commands/UndoCommandTest.java

@@ -0,0 +1,31 @@
+package seedu.address.logic.commands;
+
+import org.junit.jupiter.api.Test;
+
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandSuccess;
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandFailure;
+import static seedu.address.testutil.TypicalPersons.ALICE;
+import static seedu.address.testutil.TypicalPersons.BENSON;
+
+import seedu.address.model.AddressBookList;
+import seedu.address.model.Model;
+import seedu.address.model.ModelManager;
+
+public class UndoCommandTest {
+    private Model model = new ModelManager();
+    private UndoCommand command = new UndoCommand();
+
+    @Test
+    public void execute_undo_success() {
+        model.addPerson(ALICE);
+        model.addCommandText("add Alice");
+        model.addPerson(BENSON);
+        model.addCommandText("add Benson");
+        assertCommandSuccess(command, model, String.format(UndoCommand.MESSAGE_SUCCESS, "add Benson"), model);
+    }
+
+    @Test
+    public void execute_undo_failure() {
+        assertCommandFailure(command, model, AddressBookList.UNDO_ERROR_MESSAGE);
+    }
+}

src/test/java/seedu/address/logic/parser/AddressBookParserTest.java

@@ -25,6 +25,8 @@
 import seedu.address.logic.commands.HelpCommand;
 import seedu.address.logic.commands.LeaveCommand;
 import seedu.address.logic.commands.ListCommand;
+import seedu.address.logic.commands.RedoCommand;
+import seedu.address.logic.commands.UndoCommand;
 import seedu.address.logic.commands.ViewLeaveCommand;
 import seedu.address.logic.parser.exceptions.ParseException;
 import seedu.address.model.person.NameContainsKeywordsPredicate;
@@ -125,4 +127,13 @@ public void parseCommand_birthday_withoutMonth() throws Exception {
         assertTrue(parser.parseCommand(BirthdayCommand.COMMAND_WORD) instanceof BirthdayCommand);
     }
 
+    @Test
+    public void parseCommand_undo() throws Exception {
+        assertTrue(parser.parseCommand(UndoCommand.COMMAND_WORD) instanceof UndoCommand);
+    }
+
+    @Test
+    public void parseCommand_redo() throws Exception {
+        assertTrue(parser.parseCommand(RedoCommand.COMMAND_WORD) instanceof RedoCommand);
+    }
 }

src/test/java/seedu/address/model/AddressBookListTest.java

@@ -13,6 +13,8 @@ public void undo_success() {
         addressBookList.add(new AddressBook());
         addressBookList.add(new AddressBook());
         assertEquals(addressBookList.undo(), new AddressBook());
+        addressBookList.add(new AddressBook());
+        assertEquals(addressBookList.undo(), new AddressBook());
     }
 
     @Test