为什么不允许assertThat(map1，sameInstance(map2))？

Question

Assert.assertThat(obj1, CoreMatchers.sameInstance(obj2))

Assert.assertSame(obj1, obj2)

Assert.assertThat(map1, CoreMatchers.sameInstance(map2))

其中map类型为hashmap ，但我的测试在编译时失败：

Error:(33, 9) error: no suitable method found for assertThat(Map,Matcher<Map<String,String>>)
method Assert.<T#1>assertThat(String,T#1,Matcher<? super T#1>) is not applicable
(cannot infer type-variable(s) T#1
(actual and formal argument lists differ in length))
method Assert.<T#2>assertThat(T#2,Matcher<? super T#2>) is not applicable
(cannot infer type-variable(s) T#2
(argument mismatch; Matcher<Map<String,String>> cannot be converted to Matcher<? super Map>))
where T#1,T#2 are type-variables:
T#1 extends Object declared in method <T#1>assertThat(String,T#1,Matcher<? super T#1>)
T#2 extends Object declared in method <T#2>assertThat(T#2,Matcher<? super T#2>)
Error:(33) error: no suitable method found for assertThat(Map,Matcher<Map<String,String>>)

为什么JUnit（或Hamcrest）不能确定使用哪个匹配器？

Answer 1

结果表明，这与断言映射的标识无关--代码是正确的--但它确实与泛型有关。

我试图测试的类如下所示：

public class Response<T>{
    public final Map<String, String> map;
    public final T data;
}

然而，测试是这样写的：

@Test
public void testStuff() throws Exception {
    Map<String, String> map = new HashMap<>();
    Object data = new Object();
    Response target = new Response<>(map, data);
    assertThat(target.map, sameInstance(map));
    assertThat(target.data, sameInstance(data));
}

@Test
public void testStuff() throws Exception {
    Map<String, String> map = new HashMap<>();
    Object data = new Object();
    Response<Object> target = new Response<>(map, data);
    assertThat(target.map, sameInstance(map));
    assertThat(target.data, sameInstance(data));
}