feat: add tests for bonus exercises

src/test/java/TestEmail.java

@@ -0,0 +1,39 @@
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class TestEmail {
+    static BonusExercises ex;
+
+    @BeforeAll
+    static void setUp() {
+        ex = new BonusExercises();
+    }
+
+    @Test
+    void testEmail0() {
+        assertTrue(ex.validateEmail("john.doe@example.com"));
+    }
+
+    @Test
+    void testEmail1() {
+        assertFalse(ex.validateEmail("hello world@example.com"));
+    }
+
+    @Test
+    void testEmail2() {
+        assertTrue(ex.validateEmail("alice_bob123@research-lab.co.uk"));
+    }
+
+    @Test
+    void testEmail3() {
+        assertFalse(ex.validateEmail("user@ex_ample.com"));
+    }
+
+    @Test
+    void testEmail4() {
+        assertFalse(ex.validateEmail("user.@-example.com"));
+    }
+}