PDFUnit also runs with TestNG.

If you only use the annotation @Test no difference can be seen. Only when you expect exceptions you can see it's TestNG:

@Test(expectedExceptions=PDFUnitValidationException.class)
public void hasAuthor_NoAuthorInPDF() throws Exception {
  String filename = "documentUnderTest.pdf";
  
  AssertThat.document(filename)
            .hasAuthor()
  ;
}