diff --git a/src/test/java/seedu/address/logic/commands/AddGameCommandTest.java b/src/test/java/seedu/address/logic/commands/AddGameCommandTest.java
index cf3371929e3..698f5dbeb93 100644
--- a/src/test/java/seedu/address/logic/commands/AddGameCommandTest.java
+++ b/src/test/java/seedu/address/logic/commands/AddGameCommandTest.java
@@ -1,10 +1,15 @@
 package seedu.address.logic.commands;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static seedu.address.logic.commands.CommandTestUtil.VALID_GAME;
+import static seedu.address.logic.commands.CommandTestUtil.assertCommandFailure;
 import static seedu.address.logic.commands.CommandTestUtil.assertCommandSuccess;
+import static seedu.address.logic.commands.CommandTestUtil.showPersonAtIndex;
 import static seedu.address.testutil.TypicalIndexes.INDEX_FIRST_PERSON;
+import static seedu.address.testutil.TypicalIndexes.INDEX_SECOND_PERSON;
 import static seedu.address.testutil.TypicalPersons.getTypicalAddressBook;
 
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.Test;
 
 import seedu.address.logic.Messages;
@@ -15,7 +20,6 @@
 import seedu.address.model.UserPrefs;
 import seedu.address.model.game.Game;
 import seedu.address.model.person.Person;
-import seedu.address.testutil.EditPersonDescriptorBuilder;
 import seedu.address.testutil.GameDescriptorBuilder;
 import seedu.address.testutil.PersonBuilder;
 /**
@@ -23,17 +27,56 @@
  */
 public class AddGameCommandTest {
     private Model model = new ModelManager(getTypicalAddressBook(), new UserPrefs());
+    @AfterEach
+    public void setUp() {
+        model = new ModelManager(getTypicalAddressBook(), new UserPrefs());
+    }
     @Test
     public void execute_allFieldsSpecifiedUnfilteredList_success() {
-        Person editedPerson = new PersonBuilder().withGames(VALID_GAME).build();
-        GameDescriptor descriptor = new GameDescriptorBuilder().withGame(VALID_GAME).build();
 
-        AddGameCommand addCommand = new AddGameCommand(INDEX_FIRST_PERSON, VALID_GAME, descriptor);
+        Person personInFilteredList = model.getFilteredPersonList().get(INDEX_FIRST_PERSON.getZeroBased());
+        Person editedPerson = new PersonBuilder(personInFilteredList).withGames(VALID_GAME).build();
+
+        Model expectedModel = new ModelManager(new AddressBook(model.getAddressBook()), new UserPrefs());
+        expectedModel.setPerson(model.getFilteredPersonList().get(0), editedPerson);
 
+        GameDescriptor descriptor = new GameDescriptorBuilder().withGame(VALID_GAME).build();
+        AddGameCommand addCommand = new AddGameCommand(INDEX_FIRST_PERSON, VALID_GAME, descriptor);
         Game expectedGame = editedPerson.getGames().get(VALID_GAME);
         String expectedMessage = String.format(AddGameCommand.MESSAGE_ADD_GAME_SUCCESS, Messages.format(expectedGame));
-        Model expectedModel = new ModelManager(new AddressBook(model.getAddressBook()), new UserPrefs());
 
-        assertCommandSuccess(addCommand, model, expectedMessage, model);
+        assertCommandSuccess(addCommand, model, expectedMessage, expectedModel);
+        assertEquals(expectedGame.getGameName(), VALID_GAME);
+    }
+
+    @Test
+    public void execute_duplicatePersonUnfilteredList_failure() {
+        Person personInFilteredList = model.getFilteredPersonList().get(INDEX_FIRST_PERSON.getZeroBased());
+        Person editedPerson = new PersonBuilder(personInFilteredList).withGames(VALID_GAME).build();
+
+        model.setPerson(model.getFilteredPersonList().get(0), editedPerson);
+
+        // edit person in filtered list into a duplicate in address book
+        Person personInList = model.getAddressBook().getPersonList().get(INDEX_SECOND_PERSON.getZeroBased());
+        AddGameCommand addCommand = new AddGameCommand(INDEX_FIRST_PERSON, VALID_GAME,
+                new GameDescriptorBuilder().build());
+
+        assertCommandFailure(addCommand, model, AddGameCommand.MESSAGE_GAME_EXISTS);
+    }
+    @Test
+    public void execute_duplicatePersonFilteredList_failure() {
+        showPersonAtIndex(model, INDEX_FIRST_PERSON);
+
+        Person personInFilteredList = model.getFilteredPersonList().get(INDEX_FIRST_PERSON.getZeroBased());
+        Person editedPerson = new PersonBuilder(personInFilteredList).withGames(VALID_GAME).build();
+
+        model.setPerson(model.getFilteredPersonList().get(0), editedPerson);
+
+        // edit person in filtered list into a duplicate in address book
+        Person personInList = model.getAddressBook().getPersonList().get(INDEX_FIRST_PERSON.getZeroBased());
+        AddGameCommand addCommand = new AddGameCommand(INDEX_FIRST_PERSON, VALID_GAME,
+                new GameDescriptorBuilder().withGame(VALID_GAME).build());
+
+        assertCommandFailure(addCommand, model, AddGameCommand.MESSAGE_GAME_EXISTS);
     }
 }
diff --git a/src/test/java/seedu/address/logic/commands/CommandTestUtil.java b/src/test/java/seedu/address/logic/commands/CommandTestUtil.java
index 03a313fd736..82b1816bfc4 100644
--- a/src/test/java/seedu/address/logic/commands/CommandTestUtil.java
+++ b/src/test/java/seedu/address/logic/commands/CommandTestUtil.java
@@ -37,7 +37,7 @@ public class CommandTestUtil {
     public static final String VALID_ADDRESS_BOB = "Block 123, Bobby Street 3";
     public static final String VALID_TAG_HUSBAND = "husband";
     public static final String VALID_TAG_FRIEND = "friend";
-    public static final String VALID_GAME = "LoL";
+    public static final String VALID_GAME = "Legend League";
     public static final String VALID_GAME_USERNAME = "Potato";
     public static final String VALID_GAME_SKILLLEVEL = "Pro";
     public static final String VALID_GAME_ROLE = "Support";
diff --git a/src/test/java/seedu/address/testutil/GameBuilder.java b/src/test/java/seedu/address/testutil/GameBuilder.java
new file mode 100644
index 00000000000..d6222552829
--- /dev/null
+++ b/src/test/java/seedu/address/testutil/GameBuilder.java
@@ -0,0 +1,78 @@
+package seedu.address.testutil;
+
+
+import seedu.address.model.game.Game;
+import seedu.address.model.game.Role;
+import seedu.address.model.game.SkillLevel;
+import seedu.address.model.game.Username;
+/**
+ * A utility class to help with building Game objects.
+ */
+public class GameBuilder {
+
+    public static final String DEFAULT_GAME_NAME = "LoL";
+    public static final String DEFAULT_PHONE = "85355255";
+    public static final String DEFAULT_EMAIL = "amy@gmail.com";
+    public static final String DEFAULT_ADDRESS = "123, Jurong West Ave 6, #08-111";
+
+    private String gameName;
+    private Role role;
+    private SkillLevel skillLevel;
+    private Username username;
+    /**
+     * Creates a {@code PersonBuilder} with the default details.
+     */
+    public GameBuilder() {
+        gameName = DEFAULT_GAME_NAME;
+        role = new Role("");
+        skillLevel = new SkillLevel("");
+        username = new Username("");
+    }
+
+    /**
+     * Initializes the PersonBuilder with the data of {@code personToCopy}.
+     */
+    public GameBuilder(Game gameToCopy) {
+        gameName = gameToCopy.getGameName();
+        role = gameToCopy.getRole();
+        skillLevel = gameToCopy.getSkillLevel();
+        username = gameToCopy.getUsername();
+    }
+
+    /**
+     * Sets the {@code gameName} of the {@code Game} that we are building.
+     */
+    public GameBuilder withGameName(String gameName) {
+        this.gameName = gameName;
+        return this;
+    }
+
+    /**
+     * Sets the {@code Role} of the {@code Game} that we are building.
+     */
+    public GameBuilder withRole(String role) {
+        this.role = new Role(role);
+        return this;
+    }
+
+    /**
+     * Sets the {@code Role} of the {@code Game} that we are building.
+     */
+    public GameBuilder withSkillLevel(String skillLevel) {
+        this.skillLevel = new SkillLevel(skillLevel);
+        return this;
+    }
+
+    /**
+     * Sets the {@code Role} of the {@code Game} that we are building.
+     */
+    public GameBuilder withUsername(String username) {
+        this.username = new Username(username);
+        return this;
+    }
+
+    public Game build() {
+        return new Game(gameName, username, skillLevel, role, false);
+    }
+
+}