Mockito - ArgumentCaptor to see email content

Mockito provides a nice way to capture the arguments passed into your mocks. This works a treat when verifying the contents of an email send via a mocked JavaMailSender

ArgumentCaptor messageCapture = ArgumentCaptor.forClass(Multipart.class);
        //this is a multipart message so read all parts and verify
        StringWriter writer = new StringWriter();
        IOUtils.copy(messageCapture.getValue().getBodyPart(0).getInputStream(), writer, "UTF-8");
        String emailMessage = writer.toString();
        //verify the email doesn't contain the voucher content
        Assert.assertFalse(StringUtils.contains(emailMessage, "test content"));