@Test
@SuppressWarnings("unchecked")
public void apply() {

    final Accumulable<JdbcHighWaterMark, Long> accumulable = Mockito.mock(Accumulable.class);
    final JdbcHighWaterMarkVisitor<Long> visitor = new JdbcHighWaterMarkVisitor<>(accumulable, new IdentityFunction<Long>());
    visitor.apply(1L);
    Mockito.verify(accumulable).$plus$eq(1L);
}