如何得到在mock方法中赋的值呢？

FooService中有这么一个方法

public void doSomething(){
    ArrayList<Foo> fooList = ...;
    barService.batchAddFoos(fooList); // 批量插入

    List<String> codeList = new ArrayList<>();
    for (Foo foo : fooList) {
        codeList.add(foo.getCode());
    }
    String key = "foo_codes";
    redisService.sadd(key,codeList.toArray(new String[]{})); // 将生成的code保存到redis中
    // ...
}

BarService.batchAddFoos中会动态为code属性赋值

    for (Foo foo : foos) {
        foo.setCode(UUID.randomUUID().toString()); // dynamically generate the code value
    }

有一个单元测试测试doSomething方法

@Test
public void doSomething() throws Exception {
    fooService.doSomething();
    ArgumentCaptor<List<Foo>> fooListCaptor = ArgumentCaptor.forClass(List.class);
    verify(barService).batchAddFoos(fooListCaptor.capture());
    List<Foo> fooList = fooListCaptor.getValue();
    Assert.assertNotNull(fooList.get(0).getCode()); // 测试code是否有值
    List<String> codeList = new ArrayList<>();
    for (Foo foo : fooList) {
        codeList.add(foo.getCode());
    }
    verify(redisService).sadd("foo_codes",codeList.toArray(new String[]{}));
}

实际执行失败 因为压根就没执行batchAddFoos中的方法， 导致code属性值为空。
尝试了在测试方法中显式赋值

fooList.get(0).setCode("aaa");
fooList.get(1).setCode("bbb");

依然测试失败

Argument(s) are different! Wanted:
redisService.sadd("foo_codes", "aaa", "bbb");
Actual invocation has different arguments:
redisService.sadd("foo_codes", null, null);

像这种问题该怎么测试呢？