AssertJ有entry（）方法。你可以像这样AssertMap值。

assertThat(list)
    .extracting("myMap")
    .contains(entry("foo1", "bar1"), entry("foo2", "bar2"));

下面是javadoc：http://joel-costigliola.github.io/assertj/core/api/org/assertj/core/data/MapEntry.html

AssertMap内容的最简单方法是链接extracting方法：

MyObj o1 = new MyObj();
    o1.getMyMap().put("foo", "Hello");
    o1.getMyMap().put("bar", "Bye");
    MyObj o2 = new MyObj();
    o2.getMyMap().put("foo", "Hola");
    o2.getMyMap().put("bar", "Adios");

    List<MyObj> myObjs = Arrays.asList(o1, o2);
    assertThat(myObjs).extracting("myMap").extracting("foo").contains("Hello", "Hola");
    assertThat(myObjs).extracting("myMap").extracting("bar").contains("Bye", "Adios");

提取特征记录如下：http://joel-costigliola.github.io/assertj/assertj-core-features-highlight.html#extracted-properties-assertion
您在assertj-examples中有可执行的示例，特别是在IterableAssertionsExamples中。
希望能有所帮助！

如果你想使用containsKey方法，你必须在编译时知道键的类型（也就是说，你不能依赖于泛型）。

assertThat(list)
  .extracting("myMap")
  .asInstanceOf(InstanceOfAssertFactories.map(String.class, Long.class))
  .containsKey("key");

这有点复杂，但绝对可行：

public class Main {
    public static void main(String[] args) {
        MyObject<String, Integer> myObject1 = new MyObject<>("A", 1);
        MyObject<String, Integer> myObject2 = new MyObject<>("B", 2);
        MyObject<String, Integer> myObject3 = new MyObject<>("C", 3);

        List<MyObject<String, Integer>> myObjects = Arrays.asList(myObject1, myObject2, myObject3);

        assertThat(myObjects).extracting("myMap", Map.class).is(containingKey("A"), atIndex(0))
                                                            .is(containingKey("B"), atIndex(1))
                                                            .is(containingKey("C"), atIndex(2));
    }

    private static class MapContainsKeyCondition<K> extends Condition<Map> {
        private final K keyToContain;

        public MapContainsKeyCondition(K key) {
            this.keyToContain = key;
        }

        @Override
        public boolean matches(Map map) {
            return map.containsKey(keyToContain);
        }
    }

    private static <K> Condition<Map> containingKey(K key) {
        return new MapContainsKeyCondition<>(key);
    }

    public static class MyObject<K, V> {
        final Map<K, V> myMap;

        public MyObject(K key, V value) {
            this.myMap = Collections.singletonMap(key, value);
        }
    }
}

一种方法是从List中提取Map并验证其内容，如这里所建议的-Assertj Core Features，如下所示：

@Test
public void getMyObjList() {
    assertThat(list).isNotEmpty().extracting("myMap")
            .isNotEmpty().contains(geMap());
}

private Map<String, Integer> geMap() {
    final Map<String, Integer> map = new HashMap<>();
    map.put("A", 1);
    map.put("B", 2);
    return map;
}