Hamcrest：如何为匹配器进行实例化和强制转换？

Question

@Test
public void test() throws Exception {
    Object value = 1;
    assertThat(value, greaterThan(0));
}

简单的解决方案是通过像这样强制转换匹配器来删除泛型：

assertThat(value, (Matcher)greaterThan(0));

可能，但会生成编译器警告并感觉错误。

一个冗长的替代方案是：

@Test
public void testName() throws Exception {
    Object value = 1;

    assertThat(value, instanceOfAnd(Integer.class, greaterThan(0)));
}

private static<T> Matcher<Object> instanceOfAnd(final Class<T> clazz, final Matcher<? extends T> submatcher) {
    return new BaseMatcher<Object>() {
        @Override
        public boolean matches(final Object item) {
            return clazz.isInstance(item) && submatcher.matches(clazz.cast(item));
        }

        @Override
        public void describeTo(final Description description) {
            description
                .appendText("is instanceof ")
                .appendValue(clazz)
                .appendText(" and ")
                .appendDescriptionOf(submatcher);
        }

        @Override
        public void describeMismatch(final Object item, final Description description) {
            if (clazz.isInstance(item)) {
                submatcher.describeMismatch(item, description);
            } else {
                description
                    .appendText("instanceof ")
                    .appendValue(item == null ? null : item.getClass());
            }
        }
    };
}

Map<String, Object> map = executeMethodUnderTest();
assertThat(map, hasEntry(equalTo("the number"), greaterThan(0)));

Answer 1

这个答案不会显示如何使用Hamcrest这样做，我不知道是否有比建议的更好的方法。

但是，如果您有可能包括另一个测试库，那么AssertJ完全支持以下内容：

import org.junit.Test;

import static org.assertj.core.api.Assertions.assertThat;

public class TestClass {

  @Test
  public void test() throws Exception {
    Object value = 1;
    assertThat(value).isInstanceOfSatisfying(Integer.class, integer -> assertThat(integer).isGreaterThan(0));
  }

}

不需要任何强制转换，AssertJ为您完成此操作。

java.lang.AssertionError:
Expecting:
 <0>
to be greater than:
 <0> 

java.lang.AssertionError: 
Expecting:
 <"not an integer">
to be an instance of:
 <java.lang.Integer>
but was instance of:
 <java.lang.String>

// second constructor parameter is the light saber color
Object yoda = new Jedi("Yoda", "Green");
Object luke = new Jedi("Luke Skywalker", "Green");

Consumer<Jedi> jediRequirements = jedi -> {
  assertThat(jedi.getLightSaberColor()).isEqualTo("Green");
  assertThat(jedi.getName()).doesNotContain("Dark");
};

// assertions succeed:
assertThat(yoda).isInstanceOfSatisfying(Jedi.class, jediRequirements);
assertThat(luke).isInstanceOfSatisfying(Jedi.class, jediRequirements);

// assertions fail:
Jedi vader = new Jedi("Vader", "Red");
assertThat(vader).isInstanceOfSatisfying(Jedi.class, jediRequirements);
// not a Jedi !
assertThat("foo").isInstanceOfSatisfying(Jedi.class, jediRequirements);