Kotlin Collection

import org.junit.Test
import org.junit.Assert.*
import kotlin.math.pow
class ExampleUnitTest {
    @Test
    fun addition_isCorrect() {
        val nums = listOf(10, 20, 100, 5)
       //1. check true of false
        assert(nums.any()) // true if nums is not empty
        assert(nums.any{it > 99})
        assertFalse(nums.all { it > 99 })
        assert(nums.none{it > 101})
        // 2. filter
        assertEquals(listOf(10,5), nums.filter { it <= 10 })
        assertEquals(listOf(20,100), nums.filterNot { it <= 10 })
        // 3. map
        val ints : List<Double?> = listOf(2.0,null, 3.0)
        assertEquals(listOf(4.0, null, 9.0), ints.map { it?.pow(2) })
        assertEquals(listOf(4.0, 9.0), ints.mapNotNull { it?.pow(2) })
        //4. group
        assertEquals(mapOf("odd" to listOf(1,3), "even" to listOf(2,4)),
            listOf(1,2,3,4).groupBy { when {it % 2 == 1 ->"odd" else -> "even"} })
    }
}