MergeJsonTest.kt

  data class Entity(
    val properties: Map<String, String>,
    val count: Int
  )

  val origin = listOf(
    Entity(
      mapOf(
        "namespace1" to "first1",
        "namespace2" to "first2"
      ),
      1
    ),
    Entity(
      mapOf(
        "namespace2" to "first2",
        "namespace1" to "first1",
      ),
      1
    ),
    Entity(mapOf(), 10),
    Entity(mapOf(), 10),
    Entity(mapOf("namespace" to "first"), 1),
    Entity(mapOf("namespace" to "first"), 1),
    Entity(mapOf("namespace" to "second"), 2),
    Entity(mapOf("namespace" to "second"), 2),
    Entity(mapOf("namespace" to "third"), 3),
    Entity(mapOf("namespace" to "third"), 3),
  )

  val expected = listOf(
    Entity(
      mapOf(
        "namespace1" to "first1",
        "namespace2" to "first2"
      ),
      2
    ),
    Entity(mapOf("namespace" to "first"), 2),
    Entity(mapOf("namespace" to "third"), 6),
    Entity(mapOf("namespace" to "second"), 4),
    Entity(mapOf(), 20),
  )

  @Test
  fun mergeEntities() {

    val actual = origin
      .asSequence()
      .map { mapOf(it.properties to it) }
      .reduce { acc, element ->
        val result = acc.toMutableMap()
        element.forEach { (key, value) ->
          acc[key]?.let {
            result[key] = it.copy(count = it.count + value.count)
          } ?: run {
            result[key] = value
          }
        }
        result
      }
      .map { it.value }
      .toList()

    println("expected = $expected")
    println("actual = $actual")
    assertTrue(
      expected.size == actual.size 
          && expected.containsAll(actual) 
          && actual.containsAll(expected)
    )
  }