AssertJ：从提取列表中检索第一项将返回列表

Question

我正在尝试验证提取列表中的第一项。但是，AssertJ返回一个列表而不是从.first()返回预期的对象。

给定以下示例

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;
          }
    }
}

Answer 1

object断言的Extracting提取被测试对象（此处为Asia)属性，从而产生提取属性值的列表。您的代码只提取了一个属性，因此结果是一个值的列表，结果是该值也是一个列表，在提取之后，您最终得到的是一个元素的列表是asia.countries。