@Disabled
  @Test
  void withCount() {

    Query query = Query.of(Person.class)
            .addGroupBy(Matchers.toExpression(person.nickName))
            .addProjections(Matchers.toExpression(person.nickName))
            .withCount(true);

    assertAgg(query, "{$project: {expr0: '$nickName'}}",
            "{$group: {_id: '$expr0'}}",
            "{$count: 'count'}");
  }
Testing two field (s): {@code select distinct a, b from ...}
criteria/mongo/test/org/immutables/criteria/mongo/AggregationQueryTest.java