Added a test for the clone functionality.

rust-lib/tests/email_address_tests.rs

@@ -0,0 +1,18 @@
+use email_address_parser::EmailAddress;
+
+#[test]
+fn test_clone() {
+    let actual: EmailAddress;
+
+    {
+        let expected = EmailAddress::new("foo", "bar.com", None).unwrap();
+        actual = expected.clone();
+
+        // check they are the same
+        assert_eq!(&expected, &actual);
+    }
+
+    // ensure it exists after the source is dropped
+    assert_eq!(&"foo", &actual.get_local_part());
+    assert_eq!(&"bar.com", &actual.get_domain());
+}