@DisplayName("Test invalid usernames")
    @ValueSource(strings = { "user name", // space
            "user#name", // invalid character
            "user$name" // invalid character
    })
    void testInvalidUsernames(String username) {
        assertThrows(IllegalArgumentException.class, () -> InputValidator.validateUsername(username));
    }

    @Test
    @DisplayName("Test username length validation")