如何断言Map包含带有条目的Map

Question

我有一个需要检查嵌套映射值的单元测试。我可以通过提取条目并匹配底层Map来使断言工作，但我正在寻找一种清晰的方法来显示断言正在做什么。下面是一个非常简单的测试：

import static org.hamcrest.MatcherAssert.assertThat;
import static org.hamcrest.Matchers.hasEntry;

import java.util.HashMap;
import java.util.Map;

import org.junit.Test;

public class MapContainsMapTest {
    @Test
    public void testMapHasMap() {
        Map<String, Object> outerMap = new HashMap<String, Object>();
        Map<String, Object> nestedMap = new HashMap<String, Object>();
        nestedMap.put("foo", "bar");
        outerMap.put("nested", nestedMap);

        // works but murky
        assertThat((Map<String, Object>) outerMap.get("nested"), hasEntry("foo", "bar"));
        // fails but clear
        assertThat(outerMap, hasEntry("nested", hasEntry("foo", "bar")));
    }
}

似乎问题是使用hasEntry(K key, V value)比较外部映射，而我想使用的是hasEntry(Matcher<? super K> keyMatcher, Matcher<? super V> valueMatcher)。我不确定如何强制断言使用第二种形式。

提前谢谢。

Answer 1

我可能会为此扩展一个新的Matcher，就像这样(注意，NPE潜伏)：

class SubMapMatcher extends BaseMatcher<Map<?,?>> {

private Object key;
private Object subMapKey;
private Object subMapValue;

public SubMapMatcher(Object key, Object subMapKey, Object subMapValue) {
    super();
    this.key = key;
    this.subMapKey = subMapKey;
    this.subMapValue = subMapValue;
}

@Override
public boolean matches(Object item) {

    Map<?,?> map = (Map<?,?>)item;

    if (!map.containsKey(key)) {
        return false;
    }

    Object o = map.get(key);

    if (!(o instanceof Map<?,?>)) {
        return false;
    }

    Map<?,?> subMap = (Map<?,?>)o;
    return subMap.containsKey(subMapKey) && subMap.get(subMapKey).equals(subMapValue);
}

@Override
public void describeTo(Description description) {
    description.appendText(String.format("contains %s -> %s : %s", key, subMapKey, subMapValue));
}

public static SubMapMatcher containsSubMapWithKeyValue(String key, String subMapKey, String subMapValue) {
    return new SubMapMatcher(key, subMapKey, subMapValue);
}

}

Answer 2

如果您只想将Map<String, Object>作为值放入outerMap中，请相应地调整声明。然后你可以这样做

@Test
public void testMapHasMap() {
    Map<String, Map<String, Object>> outerMap = new HashMap<>();
    Map<String, Object> nestedMap = new HashMap<String, Object>();
    nestedMap.put("foo", "bar");
    outerMap.put("nested", nestedMap);

    Object value = "bar";
    assertThat(outerMap, hasEntry(equalTo("nested"), hasEntry("foo", value)));  
}

出于编译的原因，Object value = "bar";是必需的。或者，您可以使用

assertThat(outerMap,
   hasEntry(equalTo("nested"), Matchers.<String, Object> hasEntry("foo", "bar")));

Answer 3

如果将outerMap声明为Map<String, Map<String, Object>>，则不需要丑陋的类型转换。如下所示：

public class MapContainsMapTest {

    @Test
    public void testMapHasMap() {
        Map<String, Map<String, Object>> outerMap = new HashMap<>();
        Map<String, Object> nestedMap = new HashMap<>();
        nestedMap.put("foo", "bar");
        outerMap.put("nested", nestedMap);

        assertThat(outerMap.get("nested"), hasEntry("foo", "bar"));
    }
}