@Test
void validateMessageKeys() {

    Properties properties = new Properties();
    properties.set("key4", "value4");
    message.messages.get("zh").add(properties);
    assertThatThrownBy(() -> message.validateMessageKeys())
            .isInstanceOf(Error.class)
            .hasMessageContaining("message keys are missing for language")
            .hasMessageContaining("language=en_US");
}