Fix merge conflicts

build.gradle

@@ -62,6 +62,8 @@ dependencies {
 
     testImplementation group: 'org.junit.jupiter', name: 'junit-jupiter-api', version: jUnitVersion
 
+    testImplementation 'org.mockito:mockito-core:5.11.0'
+
     testRuntimeOnly group: 'org.junit.jupiter', name: 'junit-jupiter-engine', version: jUnitVersion
 }
 

src/test/java/seedu/address/logic/MailAppTest.java

@@ -0,0 +1,47 @@
+package seedu.address.logic;
+
+import org.junit.jupiter.api.Test;
+
+import org.mockito.MockedStatic;
+
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.mockStatic;
+import static seedu.address.testutil.TypicalPersons.GEORGE;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.when;
+
+import java.awt.Desktop;
+
+
+public class MailAppTest {
+
+    @Test
+    public void handleEmailClicked_validEmail_opensMailApp() {
+        MailApp mailApp = new MailApp(GEORGE);
+        mailApp.handleEmailClicked();
+    }
+
+    @Test
+    public void handleEmailClicked_noDesktopMailApp_throwsException() {
+        // Create a mock object for the Desktop class
+        try (MockedStatic desktopMock = mockStatic(Desktop.class)) {
+            desktopMock.when(Desktop::isDesktopSupported).thenReturn(false);
+
+            MailApp mailApp = new MailApp(GEORGE);
+            assertThrows(RuntimeException.class, () -> mailApp.handleEmailClicked());
+        }
+    }
+
+    @Test
+    public void handleEmailClicked_noMailActionSupported_throwsException() {
+        try (MockedStatic<Desktop> desktopMock = mockStatic(Desktop.class)) {
+            Desktop desktop = mock(Desktop.class);
+            when(Desktop.getDesktop()).thenReturn(desktop);
+            when(desktop.isSupported(Desktop.Action.MAIL)).thenReturn(false);
+
+            MailApp mailApp = new MailApp(GEORGE);
+
+            assertThrows(RuntimeException.class, () -> mailApp.handleEmailClicked());
+        }
+    }
+}

src/test/java/seedu/address/testutil/ContactBuilder.java

@@ -41,6 +41,7 @@ public ContactBuilder() {
         email = new Email(DEFAULT_EMAIL);
         address = new Address(DEFAULT_ADDRESS);
         gitHubUsername = new GitHubUsername(DEFAULT_GITHUB_USERNAME);
+        techStack = new HashSet<>();
         tags = new HashSet<>();
     }
 
@@ -116,5 +117,4 @@ public Contact build() {
         return new Contact(name, phone, email, address, gitHubUsername, techStack, tags);
     }
 
-
 }