@Test public void enrollsClientsOnlyOnce() {

  int before = membershipsTableSize();
  aclDAO.enrollClient(jooqContext.configuration(), client1.getId(), group2.getId());
  aclDAO.enrollClient(jooqContext.configuration(), client1.getId(), group2.getId());
  assertThat(membershipsTableSize()).isEqualTo(before + 1);
}