java - AssertJ:从提取列表中检索第一项返回列表

Question

我正在尝试验证提取列表中的第一项。然而 AssertJ 返回 List而不是 .first() 中的预期对象.

给出以下示例

public class AssertJTests
{
    @Test
    @DisplayName("Region Asia should only have one Country, Malaysia")
    public void assertRegion()
    {
        Region asia = new Region()
            .setName("Asia")
            .setCountries(Lists.newArrayList("Malaysia"));

        Consumer<Region> regionRequirement = region ->
            assertThat(region)
                .extracting(Region::getName)
                .containsOnly("Asia");

        Consumer<String> countryRequirement = country ->
            assertThat(country)
                .isEqualToIgnoringCase("Malaysia");

        assertThat(asia)
            .isInstanceOfSatisfying(Region.class, regionRequirement)
            .extracting(Region::getCountries)
            .hasSize(1)
            .first()
            .isInstanceOfSatisfying(String.class, countryRequirement);
}

    protected static class Region
    {
        private String name;

        private List<String> countries;

        List<String> getCountries()
        {
            return countries;
        }

        Region setCountries(final List<String> pCountries)
        {
            countries = pCountries;
            return this;
         }

         String getName()
         {
            return name;
         }

         Region setName(final String pName)
         {
             name = pName;
             return this;
          }
    }
}

我在期待.first()返回String但它返回 List<String> 。出现以下错误:

java.lang.AssertionError: [List check first element] Expecting: <["Malaysia"]>to be an instance of: <java.lang.String>but was instance of: <java.util.ArrayList>

Answer 1

extracting 对于 Object断言提取被测对象(此处 asia )属性，从而产生 List提取的属性值。您的代码导致仅提取一个属性，因此结果是一个值的列表，事实证明该值也是一个列表，位于 extracting 之后你最终得到的是 List一个元素是 asia.countries .