Check lists of objects for equality without order check in their List property

Question

Preconditions: I am deserializing a complex JSON into data class. The destination class has a bit of a complex hierarchy.

I have a list of objects List. Where ServiceFeature is the following (it's in kotlin, but does not matter):

data class ServiceFeature(
    val flagValue: String?,
    val effectiveFlagValue: String?,
    val name: String?,
    val attributes: List<Attribute?>?
)

As you can see ServiceFeature has an "attributes" property which includes another List of "Attribute". The main point is that Attributes in list might be in any order. Is there a reliable way to compare two lists of ServiceFeatures without order check from List<Attribute?>

I am trying to find a solution with assertJ.

Answer 1

If order does not matter for your attributes and they are unique (ie may not have multiple attributes of the same type) you might change the structure into a Set<Attribute?> instead and just use the regular compare.

If you want to preserve order but compare (unique) attributes you may convert them to set when comparing, see Easiest way to convert a List to a Set in Java .

Answer 2

If order of elements doesn't matter, then you can use Set instead of List . Having said that, You can use containsExactlyInAnyOrder() method provided by AssertJ. This method expects var-args as an argument, so in order to convert list to array we can use toTypedArray along with spread operator Eg

import org.junit.Test
import org.assertj.core.api.Assertions.*

data class ServiceFeature(
        val flagValue: String?,
        val effectiveFlagValue: String?,
        val name: String?,
        val attributes: List?
)

data class Attribute(val name: String?)

class SimpleTest {
    @Test
    fun test() {
        val list1 = listOf(ServiceFeature("flagA", "effectiveFlagA", "foo", listOf(Attribute("a"), Attribute("b"))))
        val list2 = listOf(ServiceFeature("flagA", "effectiveFlagA", "foo", listOf(Attribute("b"), Attribute("a"))))
        list1.zip(list2).forEach {
            assertThat(it.first.name).isEqualTo(it.second.name)
            assertThat(it.first.effectiveFlagValue).isEqualTo(it.second.effectiveFlagValue)
            assertThat(it.first.name).isEqualTo(it.second.name)
            val toTypedArray = it.second.attributes!!.toTypedArray() // null-check as per your need
            assertThat(it.first.attributes).containsExactlyInAnyOrder(*toTypedArray)
        }

    }
}