Hamcrest Matchers.contains matcher not working（？）

Question

我想測試一個集合是否有toString（）方法返回一個特定字符串的項目。我嘗試使用優秀的Hamcrest匹配類來做到這一點，通過組合包含Matchers.hasToString，但不知何故，其Matchers.contains不能匹配項目，即使它存在於集合中。

下面是一個例子：

class Item { 

    private String name; 

    public Item(String name){ 
     this.name = name; 
    } 

    public String toString(){ 
     return name; 
    } 
} 

// here's a sample collection, with the desired item added in the end 
Collection<Item> items = new LinkedList<Item>(){{ 
    add(new Item("a")); 
    add(new Item("b")); 
    add(new Item("c")); 
}}; 

Assert.assertThat(items, Matchers.contains(Matchers.hasToString("c"))); 

上述說法並不成功。這裏的消息：

java.lang.AssertionError: 
Expected: iterable containing [with toString() "c"] 
    but: item 0: toString() was "a" 
    at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20) 
    at org.junit.Assert.assertThat(Assert.java:865) 
    at org.junit.Assert.assertThat(Assert.java:832) 

它看起來像Matchers.contains匹配試圖遍歷列表，但Matchers.hasToString匹配的第一個項目失敗和迭代的其餘部分無效。 Matchers.contains的Hamcrest javadoc說：

「爲Iterables創建一個匹配器，匹配時檢查Iterable上的單個遍將產生滿足指定匹配器的單個項目。對於正匹配，檢查的迭代只能產生一個item「

我做錯了什麼？

Answer 1

我認爲你正在尋找Matchers.hasItem(..)

Assert.assertThat(items, Matchers.hasItem(Matchers.hasToString("c"))); 

其中規定

Creates a matcher for Iterables that only matches when a single pass over the examined Iterable yields at least one item that is matched by the specified itemMatcher . Whilst matching, the traversal of the examined Iterable will stop as soon as a matching item is found.

Matchers.contains，如你所說，

Creates a matcher for Iterables that matches when a single pass over the examined Iterable yields a single item that satisfies the specified matcher. For a positive match, the examined iterable must only yield one item.

在我看來，像在說應該只有Iterable中的一個元素。