JUnit参数化测试中assertEquals未正确判定对象相等问题求助

我正在创建测试类验证PaginationToPresentationMapper的正确性，确认映射器逻辑无误，但使用assertEquals时，系统提示实际对象与期望值指向不同引用，未判定二者相等。

测试代码 #

@RunWith(Parameterized::class)
class PaginationToPresentationMapperTest(
    private val given: PaginationDomainModel,
    private val expected: PaginationPresentationModel
) {
    companion object {
        @JvmStatic
        @Parameters(name = "Given {0} then {1}")
        fun data(): Collection<Array<*>> = listOf(
            testCase(
                nextCursor = null,
                prevCursor = null
            ),
            testCase(
                nextCursor = "next_id",
                prevCursor = null
            ),
            testCase(
                nextCursor = null,
                prevCursor = "prev_id"
            )
        )

        private fun testCase(
            nextCursor: String?,
            prevCursor: String?
        ) = arrayOf(
            PaginationDomainModel(
                nextCursor = nextCursor,
                prevCursor = prevCursor
            ),
            PaginationPresentationModel(
                nextCursor = nextCursor,
                prevCursor = prevCursor
            )
        )
    }

    private lateinit var classUnderTest: PaginationToPresentationMapper

    @Before
    fun setUp() {
        classUnderTest = PaginationToPresentationMapper()
    }

    @Test
    fun `When toPresentation`() {
        // given

        // when
        val actual = classUnderTest.toPresentation(given)

        // then
        assertEquals(expected, actual)
    }
}

失败日志 #

expected:<link.limecode.newsfeed.presentation.model.pagination.PaginationPresentationModel@7bd7d6d6> but was:<link.limecode.newsfeed.presentation.model.pagination.PaginationPresentationModel@50029372>
Expected :link.limecode.newsfeed.presentation.model.pagination.PaginationPresentationModel@7bd7d6d6
Actual   :link.limecode.newsfeed.presentation.model.pagination.PaginationPresentationModel@50029372

问题原因与解决方案 #

• 原因：Java/Kotlin中默认的equals()方法是比较对象的内存引用，而非属性值。PaginationPresentationModel类未重写equals()和hashCode()方法，导致即使两个对象的nextCursor和prevCursor属性完全一致，也会因是不同实例被判定为不相等。

• 解决方案：

  1. 推荐方案：将PaginationPresentationModel改为Kotlin的data class，data class会自动生成基于属性的equals()、hashCode()和toString()方法：

     data class PaginationPresentationModel(
         val nextCursor: String?,
         val prevCursor: String?
     )
     

  2. 手动实现：若无法改为data class，手动重写equals()和hashCode()方法，确保比较逻辑基于对象属性值：

     class PaginationPresentationModel(
         val nextCursor: String?,
         val prevCursor: String?
     ) {
         override fun equals(other: Any?): Boolean {
             if (this === other) return true
             if (javaClass != other?.javaClass) return false
     
             other as PaginationPresentationModel
     
             if (nextCursor != other.nextCursor) return false
             if (prevCursor != other.prevCursor) return false
     
             return true
         }
     
         override fun hashCode(): Int {
             var result = nextCursor?.hashCode() ?: 0
             result = 31 * result + (prevCursor?.hashCode() ?: 0)
             return result
         }
     }
     

内容的提问来源于stack exchange，提问作者Renz Salanga