SigninCard { public Attachment toAttachment() { return new Attachment() { { setContent(SigninCard.this); setContentType(CONTENTTYPE); } }; }  String getText(); void setText(String withText); List<CardAction> getButtons(); void setButtons(List<CardAction> withButtons); Attachment toAttachment(); @JsonIgnore
    static final String CONTENTTYPE; }
@Test public void testToAttachment() { Attachment attachment = card.toAttachment(); Assert.assertNotNull(attachment); Assert.assertEquals("application/vnd.microsoft.card.signin", attachment.getContentType()); }