Error messages of PDFUnit provide detailed information to support bug fixing. And they are as clear and expressive as possible. A message for an incorrect page size demonstrates this intention:

Wrong page format in 'multiple-formats-on-individual-pages.pdf' on page 1. 
Expected: 'height=297.00, width=210.00 (as 'mm')', 
but was:  'height=209.90, width=297.04 (as 'mm')'.

The position of an error is marked by the double brackets <[ and ]>. To keep error messages readable, long values are shortened. The number of dropped characters is indicated as a number in the text surrounded by '...', e.g.:

The expected content does not match the JavaScript in 'javaScriptClock.pdf'. 
Expected: '//<[Thisfileco...41...dbyPDFUnit]>', 
but was:  '//<[Constantsu...4969...);break;}}]>'.

PDFUnit comes with error message in German and English language. Write you wish to info[at]pdfunit.com if you need error messages in another language.

@Test
public void testErrorKey_hasText() throws Exception {
  try {
    String filename = PATH + "content/empty-pages.pdf";
    AssertThat.document(filename)
              .restrictedTo(EVERY_PAGE)
              .hasText()
    ;
  } catch (PDFUnitValidationException e) {
    String expectedKey = "com.pdfunit.messages.TextAvailableMessage";
    String actualKey = e.getErrorKey();
    assertEquals(expectedKey, actualKey);
  }
}