added unit tests (#864)

Author: nappy29

core-kotlin-modules/core-kotlin-lang-3/src/test/kotlin/com/baeldung/iterateDataClassProperties/IteratePropertiesOfDataClass.kt

@@ -0,0 +1,40 @@
+package com.baeldung.iterateDataClassProperties
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+
+data class Person(val name: String, val age: Int)
+class IteratePropertiesOfDataClass {
+
+    @Test
+    fun `iterate fields using destructuring declaration`() {
+        val person = Person("Robert", 28)
+        val (name, age) = person
+        assertEquals("Robert", name)
+        assertEquals(28, age)
+    }
+
+    @Test
+    fun `iterate fields using componentN methods`() {
+        val person = Person("Robert", 28)
+        val fields = listOf(person.component1(), person.component2())
+
+        assertEquals("Robert", fields[0])
+        assertEquals(28, fields[1])
+    }
+
+    @Test
+    fun `iterate fields using copy method`() {
+        val person = Person("Robert", 28)
+        var output: String? = null
+        iterateFields(person) { field -> output = field }
+
+        assertEquals("Name: Robert, Age: 28", output)
+    }
+}
+
+fun iterateFields(person: Person, action: (String) -> Unit) {
+    val defaultPerson = person.copy()
+    action("Name: ${defaultPerson.name}, Age: ${defaultPerson.age}")
+}